JSON in Oracle Database

2 JSON in Oracle Database

Oracle Database supports JSON natively with relational database features, including transactions, indexing, declarative querying, and views.

This documentation covers the use of database languages and features to work with JSON data that is stored in Oracle Database. In particular, it covers how to use SQL and PL/SQL with JSON data.

Note:

Oracle also provides a family of Simple Oracle Document Access (SODA) APIs for access to JSON data stored in the database. SODA is designed for schemaless application development without knowledge of relational database features or languages such as SQL and PL/SQL. It lets you create and store collections of documents in Oracle Database, retrieve them, and query them, without needing to know how the documents are stored in the database.

There are several implementations of SODA:

SODA for REST — Representational state transfer (REST) requests perform collection and document operations, using any language capable of making HTTP calls.
SODA for Java — Java classes and interfaces represent databases, collections, and documents.
SODA for PL/SQL — PL/SQL object types represent collections and documents.
SODA for C — Oracle Call Interface (OCI) handles represent collections and documents.
SODA for In-Database JavaScript — Oracle Database Multilingual Engine for JavaScript (MLE) objects represent collections and documents.
SODA for Node.js — Node.js classes represent collections and documents.
SODA for Python — Python objects represent collections and documents.

For complete information about SODA see Simple Oracle Document Access (SODA).

Getting Started Using JSON with Oracle Database
In general, you do the following when working with JSON data in Oracle Database: (1) create a table with a column of SQL data type JSON, (2) insert JSON data into the column, and (3) query the data in the column.
Overview of JSON in Oracle Database
Oracle Database supports JSON natively with relational database features, including transactions, indexing, declarative querying, and views. Unlike relational data, JSON data can be stored in the database, indexed, and queried without any need for a schema that defines the data.
JSON Data Type
SQL data type JSON represents JSON data using a native binary format, OSON, which is Oracle's optimized format for fast query and update in both Oracle Database server and Oracle Database clients. You can create JSON type instances from other SQL data, and conversely.
Oracle Database Support for JSON
Oracle Database support for JavaScript Object Notation (JSON) is designed to provide the best fit between the worlds of relational storage and querying JSON data, allowing relational and JSON queries to work well together. Oracle SQL/JSON support is closely aligned with the JSON support in the SQL Standard.

Parent topic: JSON Data and Oracle Database

2.1 Getting Started Using JSON with Oracle Database

In general, you do the following when working with JSON data in Oracle Database: (1) create a table with a column of SQL data type JSON, (2) insert JSON data into the column, and (3) query the data in the column.

Create a table with a primary-key column and a column of SQL data type JSON .
The following statement creates table j_purchaseorder with primary key id and with JSON column po_document.
```
CREATE TABLE j_purchaseorder
  (id          VARCHAR2 (32) NOT NULL PRIMARY KEY,
   date_loaded TIMESTAMP (6) WITH TIME ZONE,
   po_document JSON);
```
You can alternatively insert JSON data into a column that has a data type other than JSON type, such as VARCHAR2. In that case, use an is json check constraint to ensure that the data inserted into the column is well-formed JSON data. See Example 4-2.

Insert JSON data into the JSON column, using any of the methods available for Oracle Database.

The following statement uses a SQL INSERT statement to insert some simple JSON data into the third column of table j_purchaseorder (which is column po_document — see previous). Some of the JSON data is elided here (...).

INSERT INTO j_purchaseorder
  VALUES (SYS_GUID(),
          to_date('30-DEC-2014'),
          '{"PONumber"             : 1600,
            "Reference"            : "ABULL-20140421",
            "Requestor"            : "Alexis Bull",
            "User"                 : "ABULL",
            "CostCenter"           : "A50",
            "ShippingInstructions" : {...},
            "Special Instructions" : null,
            "AllowPartialShipment" : true,
            "LineItems"            : [...]}');

The SQL string '{"PONumber":1600,…}' is automatically converted to JSON data type for the INSERT operation.

Query the JSON data. The return value is always a VARCHAR2 instance that represents a JSON value. Here are some simple examples.
The following query extracts, from each document in JSON column po_document, a scalar value, the JSON number that is the value of field PONumber for the objects in JSON column po_document (see also Example 15-1):
```
SELECT po.po_document.PONumber FROM j_purchaseorder po;
```
The following query extracts, from each document, an array of JSON phone objects, which is the value of field Phone of the object that is the value of field ShippingInstructions (see also Example 15-2):
```
SELECT po.po_document.ShippingInstructions.Phone
  FROM j_purchaseorder po;
```
The following query extracts, from each document, multiple values as an array: the value of field type for each object in array Phone. The returned array is not part of the stored data but is constructed automatically by the query. (The order of the array elements is unspecified.)
```
SELECT po.po_document.ShippingInstructions.Phone.type
  FROM j_purchaseorder po;
```

Related Topics

Parent topic: JSON in Oracle Database

2.2 Overview of JSON in Oracle Database

Oracle Database supports JSON natively with relational database features, including transactions, indexing, declarative querying, and views. Unlike relational data, JSON data can be stored in the database, indexed, and queried without any need for a schema that defines the data.

(The JSON data is schemaless, even though a database schema is used to define the table and column in which it is stored. Nothing in a database schema specifies the structure of the JSON data itself.)

You can optionally validate given JSON data against a JSON schema. But most uses of JSON data do not involve JSON Schema.

JSON data has often been stored in NoSQL databases such as Oracle NoSQL Database and Oracle Berkeley DB. These allow for storage and retrieval of data that is not based on any schema, but they do not offer the rigorous consistency models of relational databases.

To compensate for this shortcoming, a relational database is sometimes used in parallel with a NoSQL database. Applications using JSON data stored in the NoSQL database must then ensure data integrity themselves.

Native support for JSON by Oracle Database obviates such workarounds. It provides all of the benefits of relational database features for use with JSON, including transactions, indexing, declarative querying, and views.

Database queries with Structured Query Language (SQL) are declarative. With Oracle Database you can use SQL to join JSON data with relational data. And you can project JSON data relationally, making it available for relational processes and tools. You can also query, from within the database, JSON data that is stored outside Oracle Database in an external table.

You can access JSON data stored in the database the same way you access other database data, including using Oracle Call Interface (OCI), and Java Database Connectivity (JDBC).

With its native binary JSON format, OSON, Oracle extends the JSON language by adding scalar types, such as date and double, which are not part of the JSON standard. SQL data type JSON uses format OSON.

Data Types for JSON Data
SQL data type JSON is Oracle's binary JSON format for fast query and update. It extends the standard JSON scalar types (number, string, Boolean, and null), to include types that correspond to SQL scalar types. This makes conversion of scalar data between JSON and SQL simple and lossless.
JSON null and SQL NULL
When both SQL code and JSON code are involved, the code and descriptions of it can sometimes be confusing when "null" is involved. Keeping JSON-language null and SQL NULL values straight requires close attention sometimes. And SQL NULL can itself be confusing.
JSON Columns in Database Tables
Oracle Database places no restrictions on the tables that can be used to store JSON documents. A column containing JSON documents can coexist with any other kind of database data. A table can also have multiple columns that contain JSON documents.
Use SQL with JSON Data
In SQL, you can create and access JSON data in Oracle Database using JSON data type constructor JSON, specialized functions and conditions, or a simple dot notation. Most of the SQL functions and conditions belong to the SQL/JSON standard, but a few are Oracle-specific.
Use PL/SQL with JSON Data
You can use JSON data type instances with PL/SQL subprograms.
Use JavaScript with JSON Data
You can use Oracle Database Multilingual Engine (MLE) to exchange JSON data between PL/SQL or SQL code and JavaScript code running in the database server. You can use the node-oracledb driver to run JavaScript code in a database client.

Related Topics

See Also:

json-schema.org for information about JSON Schema.

Parent topic: JSON in Oracle Database

2.2.1 Data Types for JSON Data

SQL data type JSON is Oracle's binary JSON format for fast query and update. It extends the standard JSON scalar types (number, string, Boolean, and null), to include types that correspond to SQL scalar types. This makes conversion of scalar data between JSON and SQL simple and lossless.

Standard JSON, as a language or notation, has predefined data types: object, array, number, string, Boolean, and null. All JSON-language types except object and array are scalar types.

The standard defines JSON data in a textual way: it is composed of Unicode characters in a standard syntax.

When actual JSON data is used in a programming language or is stored in some way, it is realized using a data type in that particular language or storage format. For example, a JDBC client application might fill a Java string with JSON data, or a database column might store JSON data using a SQL data type.

It's important to keep these two kinds of data type in mind. For example, though the JSON-language type of JSON value "abc" is string, this value can be represented, or realized, using a value of any of several SQL data types: JSON, VARCHAR2, CLOB, or BLOB.

SQL type JSON is designed specifically for JSON data. Oracle recommends that for use with Oracle Database you use JSON type for your JSON data.

JSON data type uses a binary format, OSON, which is Oracle's optimized binary JSON format for fast query and update in both Oracle Database server and Oracle Database clients. JSON type is available only if database initialization parameter compatible is at least 20.

Note:

To avoid confusion, this documentation generally refers to the types in the JSON language as "JSON-language types", and it refers to the SQL data type JSON as "JSON type". Paying close attention to this wording can help you keep straight which meaning of JSON "type" is meant in a given context.

SQL code that makes use of JSON data can include expressions in both languages, SQL and JSON. Within SQL code, literal JSON code is typically enclosed within single-quote characters ('). Paying attention to this '…' language boundary can also help understanding.

When you a SQL type other than JSON for JSON data (VARCHAR2, CLOB, or BLOB), the JSON data is said to be textual — it is unparsed character data (even when it is stored as a BLOB instance).

You can migrate existing textual JSON data in the database to JSON type data, and Oracle recommends that you do so — see Migrating Textual JSON Data to JSON Data Type.

When JSON data is of SQL data type JSON, Oracle extends the set of standard JSON-language scalar types (number, string, Boolean, and null) to include several that correspond to SQL scalar types: binary, date, timestamp, timestamp with time zone, year-month interval, day-second interval, double, and float. This enhances the JSON language, and it makes conversion of scalar data between that language and SQL simple and lossless.

When JSON data is of SQL data type VARCHAR2, CLOB, or BLOB, only the standard JSON-language scalar types are supported. But when JSON data is of SQL type JSON, Oracle Database extends the set of standard JSON-language types to include several scalar types that correspond directly to SQL scalar data types, as follows:

binary — Corresponds to SQL RAW or BLOB.
date — Corresponds to SQL DATE.
timestamp — Corresponds to SQL TIMESTAMP.
timestamp with time zone — Corresponds to SQL TIMESTAMP WITH TIME ZONE.
year-month interval — Corresponds to SQL INTERVAL YEAR TO MONTH.
day-second interval — Corresponds to SQL INTERVAL DAY TO SECOND.
double — Corresponds to SQL BINARY_DOUBLE.
float — Corresponds to SQL BINARY_FLOAT.

Note:

You can use the JSON path-expression item method type() to determine the JSON-language type of any JSON scalar value.

It returns the type name as one of these JSON strings: "binary", "date", "timestamp", "timestamp with time zone","yearmonthInterval", "daysecondInterval", "double", "float", "number", "null", "string", "boolean". For example, if the targeted scalar JSON value is of type timestamp with time zone then type() returns the string "timestamp with time zone". See:

Here are some ways to obtain JSON scalar values of such Oracle-specific JSON-language types in your JSON data that is stored as JSON type:

Use SQL/JSON generation functions with RETURNING JSON. Scalar SQL values used in generating array elements or object field values result in JSON scalar values of corresponding JSON-language types. For example, a BINARY_FLOAT SQL value results in a float JSON value.
Use Oracle SQL function json_scalar. For example, applying it to a BINARY_FLOAT SQL value results in a float JSON value.
Use a database client with client-side encoding to create an Oracle-specific JSON value as JSON type before sending that to the database.
Instantiate PL/SQL object types for JSON with JSON data having Oracle-specific JSON scalar types. This includes updating existing such object-type instances.
Use PL/SQL method to_json() on a PL/SQL DOM instance (JSON_ELEMENT_T instance).

Here are some ways to make use of JSON scalar values of Oracle-specific JSON-language types:

Use SQL/JSON condition json_exists, comparing the value of a SQL bind variable with the result of applying an item method that corresponds to an Oracle-specific JSON scalar type.
Use SQL/JSON function json_value with a RETURNING clause that returns a SQL type that corresponds to an Oracle-specific JSON scalar type.

Related Topics

Parent topic: Overview of JSON in Oracle Database

2.2.2 JSON null and SQL NULL

When both SQL code and JSON code are involved, the code and descriptions of it can sometimes be confusing when "null" is involved. Keeping JSON-language null and SQL NULL values straight requires close attention sometimes. And SQL NULL can itself be confusing.

In the JSON language, null is both a value and the name of a (JSON-language) type. Type null has only one possible value, null.
In SQL, each data type has a NULL value. There is a NULL value for type VARCHAR2, one for type NUMBER, …, and one for type JSON (Oracle's native binary format for JSON data).

NULL in SQL typically represents the absence of a value (missing, unknown, or inapplicable data). But SQL does not distinguish the absence of a value from the presence of a (SQL) NULL value.

A SQL value can hold a scalar JSON-language value, and JSON null is one such value. The SQL value in this case is non-NULL (of whatever SQL type is being used to hold the JSON data).

When a JSON-type instance (for example, a row of a JSON-type column) has the SQL value NULL it generally means that there is no JSON data present in that instance.

A JSON value of null is a non-NULL value as far as SQL is concerned; it is not the SQL value NULL. In particular, SQL condition IS NULL returns false for a JSON null value, and SQL condition IS NOT NULL returns true. And SQL/JSON condition json_exists returns true when the value whose existence it tests for is JSON null.

SQL/JSON function json_value extracts a SQL scalar value from its input JSON data. If the value to be extracted is JSON null, then, by default, json_value returns SQL NULL. (You can override this behavior for a given use of json_value by using an ON ERROR handling clause or an ON EMPTY handling clause.)

The same is not true, however, for SQL/JSON function json_query or for a simple-dot-notation query. Those return JSON data. If your database supports JSON data type, and if the value to be extracted is JSON null then they both return that existing JSON null value as such; that is, they return what json_scalar('null') returns.

Remember that the purpose of json_value is to return a SQL scalar value that corresponds to a JSON scalar value that you extract from some JSON data. There is no SQL scalar value that corresponds to JSON null in the same way that, say, SQL value TRUE corresponds to JSON true or SQL number 42 corresponds to JSON number 42. Oracle JSON data type has a null scalar value, but SQL does not have any equivalent scalar value.

Q: What's the SQL type of the JSON value null?

A: That depends on the code/context. It could be any SQL type that you can use to store JSON data — see Data Types for JSON Data.

Q: What determines the order of JSON null values and SQL NULL values, if both are present in a query result set?

A: By default, returned rows containing SQL NULL values are last in the sequence when sorting in ascending order, and they are first when sorting in descending order. You can use keywords NULLS FIRST or NULLS LAST to override this default behavior. See SELECT in Oracle Database SQL Language Reference.

When you extract a scalar value from JSON data, the following can occur:

The input JSON data itself is (SQL) NULL, so no value is selected. This is the case when a row of data is NULL, for example.
The input JSON data is not (SQL) NULL but the query (path expression, for example) does not select any scalar value — the targeted value is missing.
The query selects a JSON null value.

The behavior for Case 3 depends on whether your database supports JSON data type, that is, whether the value of initialization parameter compatible is at least 20.

All data in Table 2-1 is SQL data. Uppercase NULL indicates a SQL NULL value. JSON data shown indicates the content of a SQL type (such as VARCHAR2 or JSON) that can contain JSON data. A JSON-language null value is written in lowercase.

Table 2-1 Handling of SQL NULL, missing, and JSON null Input for JSON-Type Data

Case	JSON Input Data	Dot Notation .a	JSON_VALUE('$.a')	JSON_QUERY('$.a')
Case 1: input data is `NULL`	`NULL`	`NULL`	`NULL`	`NULL`
Case 2: targeted data is missing	`{}`	`NULL`	`NULL`	`NULL`
Case 3, with `JSON` type support: JSON `null` value selected	`{"a":null}`	With `JSON` type input: `JSON` type `null` value (the same thing that `json_scalar('null')` returns) Otherwise: `NULL`	`NULL`	With either `JSON` type input or `RETURNING JSON`: `JSON` type `null` value (same thing that `json_scalar('null')` returns) Otherwise: the textual JSON `null` value of the `RETURNING` or input type (same thing that `json_serialize(json_scalar('null'))` returns)
Case 3, without `JSON` type support: JSON `null` value selected	`{"a":null}`	`NULL`	`NULL`	`NULL`

Note:

Oracle SQL NULL can itself be a bit confusing. Except for the large-object (LOB) data types (BLOB, (N)CLOB, and BFILE), Oracle SQL types that can have zero-length values do not distinguish a zero-length value from the NULL value. Such types include RAW and the character types, such as (N)VARCHAR(2) and (N)CHAR. This means, in effect, that an "empty string" value in such a type is no different from the NULL value of that type.

Related Topics

Parent topic: Overview of JSON in Oracle Database

2.2.3 JSON Columns in Database Tables

Oracle Database places no restrictions on the tables that can be used to store JSON documents. A column containing JSON documents can coexist with any other kind of database data. A table can also have multiple columns that contain JSON documents.

When using Oracle Database as a JSON document store, your tables that contain JSON columns typically also have a few non-JSON housekeeping columns. These typically track metadata about the JSON documents.

If you use JSON data to add flexibility to a primarily relational application then some of your tables likely also have a column for JSON documents, which you use to manage the application data that does not map directly to your relational model.

Oracle recommends that you use data type JSON for JSON columns. If you instead use textual JSON storage (VARCHAR2, CLOB, or BLOB) then Oracle recommends that you use an is json check constraint to ensure that column values are valid JSON instances (see Example 4-2).

By definition, textual JSON data is encoded using a Unicode encoding, either UTF-8 or UTF-16. You can use VARCHAR2 or CLOB data that is stored in a non-Unicode character set as if it were JSON data, but in that case Oracle Database automatically converts the character set to UTF-8 when processing the data.

Data stored using data type JSON or BLOB is independent of character sets and does not undergo conversion when processing the data.

Parent topic: Overview of JSON in Oracle Database

2.2.4 Use SQL with JSON Data

In SQL, you can create and access JSON data in Oracle Database using JSON data type constructor JSON, specialized functions and conditions, or a simple dot notation. Most of the SQL functions and conditions belong to the SQL/JSON standard, but a few are Oracle-specific.

SQL/JSON query functions json_value, json_query, and json_table.

These evaluate SQL/JSON path expressions against JSON data to produce SQL values.
Oracle SQL condition json_textcontains and SQL/JSON conditions json_exists, is json, and is not json.

Condition json_exists checks for the existence of given JSON data; json_textcontains provides full-text querying of JSON data; and is json and is not json check whether given JSON data is well-formed.

json_exists and json_textcontains check the data that matches a SQL/JSON path expression.
A simple dot notation that acts similar to a combination of query functions json_value and json_query.

This resembles a SQL object access expression, that is, attribute dot notation for an abstract data type (ADT). This is the easiest way to query JSON data in the database.
SQL/JSON generation functions json_object, json_array, json_objectagg, and json_arrayagg.

These gather SQL data to produce JSON object and array data (as a SQL value).
Oracle SQL functions json_serialize and json_scalar, and Oracle SQL condition json_equal.

Function json_serialize returns a textual representation of JSON data; json_scalar returns a JSON type scalar value that corresponds to a given SQL scalar value; and json_equal tests whether two JSON values are the same.
JSON data type constructor JSON.

This parses textual JSON data to create an instance of SQL data type JSON.
Oracle SQL aggregate function json_dataguide.

This produces JSON data that is a data guide, which you can use to discover information about the structure and content of other JSON data in the database.

As a simple illustration of querying, here is a dot-notation query of the documents stored in JSON column po_document of table j_purchaseorder (aliased here as po). It obtains all purchase-order requestors (JSON field Requestor).

SELECT po.po_document.Requestor FROM j_purchaseorder po;

Parent topic: Overview of JSON in Oracle Database

2.2.5 Use PL/SQL with JSON Data

You can use JSON data type instances with PL/SQL subprograms.

You can manipulate JSON data within PL/SQL code using SQL code or PL/SQL object types.

You can generally use SQL code, including SQL code that accesses JSON data, within PL/SQL code.

The following SQL functions and conditions are also available as built-in PL/SQL functions: json_value, json_query, json_object, json_array, json_scalar, json_serialize, json_exists, is json, is not json, and json_equal.

There are also PL/SQL object types for JSON, which you can use for fine-grained construction and manipulation of In-Memory JSON data. You can construct object-type data, introspect it, modify it, compare it, sort it, and serialize it back to textual JSON data.

You can use JSON data type instances as input and output of PL/SQL subprograms. You can manipulate JSON-type data in PL/SQL by instantiating JSON object types, such as JSON_OBJECT_T.

Oracle Database prior to Release 23c has no BOOLEAN data type. But for all Oracle Database releases PL/SQL has a BOOLEAN data type. For PL/SQL (as well as for SQL, starting with Release 23c):

json_exists, is json, is not json, and json_equal are Boolean functions.
json_value can return a BOOLEAN value. json_table columns with json_value semantics can be of type BOOLEAN.
json_scalar can accept a BOOLEAN value as argument, in which case it returns a Boolean JSON type instance (true or false).
json_object, json_objectagg, json_array, and json_arrayagg can generate JSON objects and arrays that contain values true and false, corresponding to PL/SQL values TRUE and FALSE.

Similarly, if you pass SQL TRUE or FALSE to json_transform then these are mapped to JSON true and false if included in the transformation result.
json_exists and json_transform can use BOOLEAN bind variables.

Using PL/SQL you can create JSON schemas from relational or object-relational data.

PL/SQL also provides subprograms to use JSON Schema, in package DBMS_JSON_SCHEMA:

You can validate JSON data against a JSON schema using PL/SQL function or procedure DBMS_JSON_SCHEMA.is_valid(). The function returns 1 for valid and 0 for invalid (invalid data can optionally raise an error). The procedure returns TRUE for valid and FALSE for invalid as the value of an OUT parameter.
You can use PL/SQL function DBMS_JSON_SCHEMA.validate_report to read a validity-check error report.
You can use PL/SQL function DBMS_JSON_SCHEMA.is_schema_valid to check whether a given JSON schema is itself valid according to the JSON Schema standard.
You can use PL/SQL function DBMS_JSON_SCHEMA.describe to generate a JSON schema from a table, view, object type, or collection type, or from a synonym that resolves to one of those.

See Also:

json-schema.org for information about JSON Schema

Parent topic: Overview of JSON in Oracle Database

2.2.6 Use JavaScript with JSON Data

You can use Oracle Database Multilingual Engine (MLE) to exchange JSON data between PL/SQL or SQL code and JavaScript code running in the database server. You can use the node-oracledb driver to run JavaScript code in a database client.

MLE runs JavaScript code dynamically using (1) PL/SQL package DBMS_MLE and (2) MLE modules that persist in the database. Using MLE modules generally offers more flexibility and a better way of separating JavaScript code from PL/SQL code. MLE modules are analogous to PL/SQL packages, the difference being that the code is JavaScript instead of PL/SQL.

You can exchange JSON data between JavaScript code running in the database server and database storage in these ways:

Use server-side MLE JavaScript driver mle-js-oracledb.
Use JavaScript stored subprograms that refer to an MLE module. Subprogram arguments (IN, OUT, INOUT) and return values can be of JSON data type.
Use procedures in PL/SQL package DBMS_MLE to exchange JSON values between PL/SQL code and JavaScript code.

The data-type mappings used by server-side MLE JavaScript driver mle-js-oracledb, between JSON values (objects, arrays, and scalars) and JavaScript values, are generally aligned with the mappings used by client-side JavaScript driver node-oracledb. The mappings between scalar values differ in some respects however — see MLE Type Conversions.

You can use PL/SQL procedure DBMS_MLE.export_to_mle to export JSON data from PL/SQL to a dynamic MLE execution context, and then use it there with JavaScript code. In the other direction, you can use PL/SQL procedure DBMS_MLE.import_from_mle to import objects from MLE JavaScript code to PL/SQL, and then use them in PL/SQL as JSON objects.

You use JavaScript function importValue() from built-in module mle-js-bindings to import, into the current dynamic MLE execution context, a value that was previously exported along with a JavaScript variable name, using PL/SQL procedure DBMS_MLE.export_to_mle. Function importValue() takes that variable name as argument and returns a JavaScript value, with all scalar values of the JSON data converted to the corresponding native JavaScript type.

Similarly, you use JavaScript function exportValue() to export a value from the current dynamic MLE execution context.

See Also:

Overview of Dynamic MLE Execution in Oracle Database JavaScript Developer's Guide
MLE JavaScript Functions in Oracle Database JavaScript Developer's Guide
MLE Type Conversions in Oracle Database JavaScript Developer's Guidefor information about data-type conversions between JavaScript and PL/SQL or SQL, including to and from JSON-language types represented in SQL data type JSON.
MLE Modules on GitHub for information about mle-js-oracledb and mle-js-bindings
Node.js node-oracledb on GitHub

Parent topic: Overview of JSON in Oracle Database

2.3 JSON Data Type

SQL data type JSON represents JSON data using a native binary format, OSON, which is Oracle's optimized format for fast query and update in both Oracle Database server and Oracle Database clients. You can create JSON type instances from other SQL data, and conversely.

The other SQL data types that support JSON data, besides JSON type, are VARCHAR2, CLOB, and BLOB. This non-JSON type data is called textual, or serialized, JSON data. It is unparsed character data (even when stored as a BLOB instance, as the data is a sequence of UTF-8 encoded bytes).

Using data type JSON avoids costly parsing of textual JSON data and provides better query performance.

You can convert textual JSON data to JSON type data by parsing it with type constructor JSON. JSON text that you insert into a database column of type JSON is parsed implicitly — you need not use the constructor explicitly.

In the other direction, you can convert JSON type data to textual JSON data using SQL/JSON function json_serialize. JSON type data that you insert into a database column of a JSON textual data type (VARCHAR2, CLOB, or BLOB) is serialized implicitly — you need not use json_serialize explicitly.

Regardless of whether the JSON type data uses Oracle-specific scalar JSON types (such as date), the resulting serialized JSON data always conforms to the JSON standard.

You can create complex JSON type data from non-JSON type data using the SQL/JSON generation functions: json_object, json_array, json_objectagg, and json_arrayagg.

You can create a JSON type instance with a scalar JSON value using Oracle SQL function json_scalar. In particular, the value can be of an Oracle-specific JSON-language type, such as a date, which is not part of the JSON standard.

In the other direction, you can use SQL/JSON function json_value to query JSON type data and return an instance of a SQL object type or collection type.

JSON data type, its constructor JSON, and Oracle SQL function json_scalar can be used only if database initialization parameter compatible is at least 20. Otherwise, trying to use any of them raises an error.

JSON Data Type Constructor
The JSON data type constructor, JSON, takes as input a textual JSON value (a scalar, object, or array), parses it, and returns the value as an instance of JSON type. Alternatively, the input can be an instance of a user-defined PL/SQL or SQL aggregate type.
Oracle SQL Function JSON_SCALAR
Oracle SQL function json_scalar accepts a SQL scalar value as input and returns a corresponding JSON scalar value as a JSON type instance. In particular, the value can be of an Oracle-specific JSON-language type (such as a date), which is not part of the JSON standard.
Oracle SQL Function JSON_SERIALIZE
Oracle SQL function json_serialize takes JSON data (of any SQL data type, JSON, VARCHAR2, CLOB, or BLOB) as input and returns a textual representation of it (as VARCHAR2, CLOB, or BLOB data). VARCHAR2(4000) is the default return type.
JSON Constructor, JSON_SCALAR, and JSON_SERIALIZE: Summary
Relations among JSON data type constructor JSON, Oracle SQL function json_scalar, and Oracle SQL function json_serialize are summarized.
Textual JSON Objects That Represent Extended Scalar Values
Native binary JSON data (OSON format) extends the JSON language by adding scalar types, such as date, that correspond to SQL types and are not part of the JSON standard. Oracle Database also supports the use of textual JSON objects that represent JSON scalar values, including such nonstandard values.
Comparison and Sorting of JSON Data Type Values
The canonical sort order for values of SQL data type JSON is described. It is used to compare all JSON values.

Related Topics

See Also:

Oracle Database SQL Language Reference for information about JSON data type
Oracle Database SQL Language Reference for information about constructor JSON
Oracle Database SQL Language Reference for information about Oracle SQL function json_scalar
Oracle Database SQL Language Reference for information about Oracle SQL function json_serialize

Parent topic: JSON in Oracle Database

2.3.1 JSON Data Type Constructor

The JSON data type constructor, JSON, takes as input a textual JSON value (a scalar, object, or array), parses it, and returns the value as an instance of JSON type. Alternatively, the input can be an instance of a user-defined PL/SQL or SQL aggregate type.

Note:

You can use constructor JSON only if database initialization parameter compatible is at least 20. Otherwise, the constructor raises an error (regardless of what input you pass it).

For example, given SQL string '{}' as input, the JSON type instance returned is the empty object {}. The input '{a : {"b":"beta", c:[+042, "gamma",]},}' results in the JSON instance {"a":{"b":"beta","c":[42,"gamma"]}}.

(Note that this contrasts with the behavior of Oracle SQL function json_scalar, which does not parse textual input but just converts it to a JSON string value: json_scalar('{}') returns the JSON string "{}". To produce the same JSON string using constructor JSON, you must add explicit double-quote characters: JSON('"{}"').)

Textual input to constructor JSON can be either a literal SQL string or data of type VARCHAR2, CLOB, or BLOB. A SQL NULL value as input results in a JSON type instance of SQL NULL.

Non-textual input to the constructor can be an instance of any of the following user-defined data types:

PL/SQL Varray
PL/SQL record
SQL object type
PL/SQL index by binary_integer collection (IBBI)
PL/SQL nested table
PL/SQL associative array

A varray instance as argument results in a JSON array. The JSON-array elements are created from the elements of the varray collection (in order).

Each of the other instances results in a JSON object. The JSON-object members are created from the attributes of a record instance or a SQL object instance, the indexes of an IBBI or nested-table instance, and the key–value pairs of an associative-array instance.

The value returned by the constructor can be any JSON value that is supported by Oracle. This includes values of the standard JSON-language types: object, array, string, Boolean, null, and number. It also includes any non-standard Oracle scalar JSON values, that is, values of the Oracle-specific scalar types: double, float, binary, date, timestamp, day-second interval, and year-month interval. If the constructor is used with keyword EXTENDED then the values of the Oracle-specific types can be derived from Oracle extended-object patterns in the textual JSON input.

If the textual input is not well-formed JSON data then an error is raised. This includes the case where it has one or more objects in it that have duplicate field (key) names. It can, however, have lax JSON syntax. Other than this syntax relaxation, to be well-formed the input data must conform to RFC 8259.

If you need to ensure that the textual input uses only strict JSON syntax then use SQL condition is json to filter it. This code prevents acceptance of non-strict syntax:

SELECT JSON(jcol) FROM table WHERE jcol is json (STRICT);

As a convenience, when using textual JSON data to perform an INSERT or UPDATE operation on a JSON type column, the textual data is implicitly wrapped with constructor JSON.

Use cases for constructor JSON include on-the-fly parsing and conversion of textual JSON data to JSON type. (An alternative is to use condition is json in a WHERE clause.) You can pass the constructor a bind variable with a string value or data from an external table, for instance.

As one example, you can use constructor JSON to ensure that textual data that is not stored in the database with an is json check constraint is well-formed. You can then use the simple dot-notation query syntax with the resulting JSON type data. (You cannot use the dot notation with data that is not known to be well-formed.) Example 2-1 illustrates this.

Example 2-1 Converting Textual JSON Data to JSON Type On the Fly

This example uses simple dot-notation syntax to select a field from some textual JSON data that is not known to the database to be well-formed. It converts the data to JSON type data, before selecting. Constructor JSON raises an error if its argument is not well-formed. (Note that dot-notation syntax requires the use of a table alias — j in this case.)

WITH jtab AS
  (SELECT JSON(
     '{ "name" : "Alexis Bull",
        "Address": { "street" : "200 Sporting Green",
                     "city" : "South San Francisco",
                     "state" : "CA",
                     "zipCode" : 99236,
                     "country" : "United States of America" } }')
     AS jcol FROM DUAL)
  SELECT j.jcol.Address.city FROM jtab j;

Related Topics

See Also:

JSON Type Constructor in Oracle Database SQL Language Reference for information about constructor JSON
PL/SQL and JSON Type Conversions in Oracle Database PL/SQL Language Reference for information about the conversion of a non-textual argument to a JSON-type value

Parent topic: JSON Data Type

2.3.2 Oracle SQL Function JSON_SCALAR

Oracle SQL function json_scalar accepts a SQL scalar value as input and returns a corresponding JSON scalar value as a JSON type instance. In particular, the value can be of an Oracle-specific JSON-language type (such as a date), which is not part of the JSON standard.

You can use function json_scalar only if database initialization parameter compatible is at least 20. Otherwise it raises an error.

You can think of json_scalar as a scalar generation function. Unlike the SQL/JSON generation functions, which can return any SQL data type that supports JSON data, json_scalar always returns an instance of JSON type.

The argument to json_scalar can be an instance of any of these SQL data types: JSON, BLOB, CLOB, NCLOB, VARCHAR2, VARCHAR, NVARCHAR2, CHAR, NCHAR, RAW, BOOLEAN, DATE, TIMESTAMP, TIMESTAMP WITH TIME ZONE, INTERVAL YEAR TO MONTH. INTERVAL DAY TO SECOND, NUMBER, BINARY_DOUBLE, or BINARY_FLOAT.

The returned JSON type instance is a JSON-language scalar value supported by Oracle. For example, json_scalar(current_timestamp) returns an Oracle JSON value of type timestamp (as an instance of SQL data type JSON).

With JSON type input, json_scalar behaves as follows:

Input that corresponds to a JSON scalar value is simply returned.
Input that corresponds to a JSON nonscalar value results in an error. If the error handler is NULL ON ERROR, which it is by default, then SQL NULL (of JSON data type) is returned.

Tip:

Because json_scalar returns NULL by default for nonscalar input, and because comparison involving a nonscalar JSON value can be more costly than scalar-with-scalar comparison, a simple manual optimization when ordering or comparing JSON data is to do so after wrapping it with json_scalar, thus effectively pruning nonscalars from the data to be compared. (More precisely, they are replaced with NULL, which is quickly compared.)

For example instead of this:

SELECT data FROM customers c
  ORDER BY c.data.revenue;

Use this:

SELECT data FROM customers c
  ORDER BY json_scalar(c.data.revenue);

Note:

You can use the JSON path-expression item method type() to determine the JSON-language type of any JSON scalar value.

Table 2-2 JSON_SCALAR Type Conversion: SQL Types to Oracle JSON Types

SQL Type (Source)	JSON Language Type (Destination)
`VARCHAR2`, `VARCHAR`, `NVARCHAR2`, `CHAR`, or `NCHAR`	string
`CLOB` or `NCLOB`	string
`BLOB`	binary
`RAW`	binary
`BOOLEAN`	boolean
`NUMBER`	number (or string if infinite or undefined value)
`BINARY_DOUBLE`	double (or string if infinite or undefined value)
`BINARY_FLOAT`	float (or string if infinite or undefined value)
`DATE`	date
`TIMESTAMP`	timestamp
`TIMESTAMP WITH TIME ZONE`	timestamp with time zone
`INTERVAL DAY TO SECOND`	daysecondInterval
`INTERVAL YEAR TO MONTH`	yearmonthInterval

An exception are the numeric values of positive and negative infinity, and values that are the undefined result of a numeric operation ("not a number" or NaN) — they cannot be expressed as JSON numbers. For those, json_scalar returns not numeric-type values but the JSON strings "Inf", "-Inf", and "Nan", respectively.

A JSON type value returned by json_scalar remembers the SQL data type from which it was derived. If you then use json_value (or a json_table column with json_value semantics) to extract that JSON type value, and you use the corresponding type-conversion item method, then the value extracted has the original SQL data type. For example, this query returns a SQL TIMESTAMP value:

SELECT json_value(json_scalar(current_timestamp), '$.timestamp()')
  FROM DUAL;

Note that if the argument is a SQL string value (VARCHAR2. VARCHAR, NVARCHAR, CHAR, NCHAR, or CLOB) then json_scalar simply converts it to a JSON string value. It does not parse the input as JSON data.

For example, json_scalar('{}') returns the JSON string value "{}". Because constructor JSON parses a SQL string, it returns the empty JSON object {} for the same input. To produce the same JSON string using constructor JSON, the double-quote characters must be explicitly present in the input: JSON('"{}"').

If the argument to json_scalar is a SQL NULL value then you can obtain a return value of SQL NULL (the default behavior) or JSON null (using keywords JSON NULL ON NULL). (The default behavior of returning SQL NULL is the only exception to the rule that a JSON scalar value is returned.)

Note:

Be aware that, although function json_scalar preserves timestamp values, it drops any time-zone information from a timestamp. The time-zone information is taken into account by converting to UTC time. See Table 2-4.

If you need to add explicit time-zone information as JSON data then record it separately from a SQL TIMESTAMP WITH TIME ZONE instance and pass that to a JSON generation function. Example 2-2 illustrates this.

Example 2-2 Adding Time Zone Information to JSON Data

This example inserts a TIMESTAMP WITH TIME ZONE value into a table, then uses generation function json_object to construct a JSON object. It uses SQL functions json_scalar and extract to provide the JSON timestamp and numeric time-zone inputs for json_object.

CREATE TABLE t (tz TIMESTAMP WITH TIME ZONE);
  INSERT INTO t
    VALUES (to_timestamp_tz('2019-05-03 20:00:00 -8:30',
                            'YYYY-MM-DD HH24:MI:SS TZH:TZM'));

-- This query returns the UTC timestamp value "2019-05-04T04:30:00"
SELECT json_scalar(tz) FROM t;

-- Create a JSON object that has 3 fields:
--  timestamp:       JSON timestamp value (UTC time): 
--  timeZoneHours:   hours component of the time zone, as a JSON number
--  timeZoneMinutes: minutes component of the time zone, as a JSON number

SELECT json_object('timestamp'       : json_scalar(tz),
                   'timezoneHours'   : extract(TIMEZONE_HOUR FROM tz),
                   'timezoneMinutes' : extract(TIMEZONE_MINUTE FROM tz))
  FROM t;

-- That query returns a JSON object and prints it in serialized form.
-- The JSON timestamp value is serialized as an ISO 8601 date-time string.
-- The time-zone values (JSON numbers) are serialized as numbers.
--
-- {"timestamp"       : "2019-05-04T04:30:00",
--  "timezoneHours"   : -8,
--  "timezoneMinutes" : -30}

Related Topics

See Also:

Oracle Database SQL Language Reference in Oracle Database SQL Language Reference for information about Oracle SQL function json_scalar
JSON Data Type in Oracle Database SQL Language Reference
Character Data Types in Oracle Database SQL Language Reference for information about SQL data types CHAR, NCHAR, VARCHAR2, VARCHAR, and NVARCHAR2
Large Object (LOB) Data Types in Oracle Database SQL Language Reference for information about SQL data types BLOB, CLOB, and NCLOB
Numeric Data Types in Oracle Database SQL Language Reference for information about SQL data types NUMBER, BINARY_DOUBLE, and BINARY_FLOAT
Datetime and Interval Data Types in Oracle Database SQL Language Reference for information about SQL data types DATE, TIMESTAMP, TIMESTAMP WITH TIME ZONE, INTERVAL YEAR TO MONTH, and INTERVAL DAY TO SECOND
Boolean Data Type in Oracle Database SQL Language Reference
RAW and LONG RAW Data Types in Oracle Database SQL Language Reference for information about SQL data type RAW

Parent topic: JSON Data Type

2.3.3 Oracle SQL Function JSON_SERIALIZE

Oracle SQL function json_serialize takes JSON data (of any SQL data type, JSON, VARCHAR2, CLOB, or BLOB) as input and returns a textual representation of it (as VARCHAR2, CLOB, or BLOB data). VARCHAR2(4000) is the default return type.

You typically use json_serialize to transform the result of a query. The function supports an error clause and a returning clause. You can optionally do any combination of the following:

Automatically escape all non-ASCII Unicode characters, using standard ASCII Unicode escape sequences (keyword ASCII).
Pretty-print the result (keyword PRETTY).
Order the members of objects in the result — ascending alphabetical order by field name (keyword ORDERED).

The order is defined by the VARCHAR2 collation with binary ordering as represented in the AL32UTF8 character set. Put differently, characters are ordered according to their Unicode code points.
Truncate the result to fit the return type (keyword TRUNCATE).
Translate values of Oracle-specific scalar JSON-language types to Oracle extended-object patterns (keyword EXTENDED).

See Example 2-3 and Example 2-4.

By default, function json_serialize always produces JSON data that conforms to the JSON standard (RFC 8259), in which case the returned data uses only the standard data types of the JSON language: object, array, and the scalar types string, number, Boolean, and null.

The stored JSON data that gets serialized can also have values of scalar types that Oracle has added to the JSON language. JSON data of such types is converted when serialized according to Table 2-3. For example, a numeric value of JSON-language type double is serialized by converting it to a textual representation of a JSON number.

Note:

Input JSON string values are returned verbatim (no change). If you want to serialize a nonstring scalar JSON value using a different format from what is specified here, then first use a SQL conversion function such as to_char to produce the string value formatted as you want, and pass that value to json_serialize.

Table 2-3 JSON_SERIALIZE Converts Oracle JSON-Language Types To Standard JSON-Language Types

Oracle JSON Scalar Type (Reported by type())	Standard JSON Scalar Type	Notes
binary	string	Conversion is equivalent to the use of SQL function `rawtohex`: Binary bytes are converted to hexadecimal characters representing their values.
date	string	The string is in an ISO 8601 date format: YYYY-MM-DD. For example: `"2019-05-21"`.
daysecondInterval	string	The string is in an ISO 8601 duration format that corresponds to a ds_iso_format specified for SQL function `to_dsinterval`. PdDThHmMsS, where d, h, m, and s are digit sequences for the number of days, hours, minutes, and seconds, respectively. For example: `"P0DT06H23M34S"`. s can also be an integer-part digit sequence followed by a decimal point and a fractional-part digit sequence. For example: `P1DT6H23M3.141593S`. Any sequence whose value would be zero is omitted, along with its designator. For example: `"PT3M3.141593S"`. However, if all sequences would have zero values then the syntax is `"P0D"`.
double	number	Conversion is equivalent to the use of SQL function `to_number`.
float	number	Conversion is equivalent to the use of SQL function `to_number`.
timestamp	string	The string is in an ISO 8601 date-with-time format: YYYY-MM-DDThh:mm:ss.ssssss. For example: `"2019-05-21T10:04:02.340129"`.
timestamp with time zone	string	The string is in an ISO 8601 date-with-time format: YYYY-MM-DDThh:mm:ss.ssssss(+\|-)hh:mm or, for a zero offset from UTC, YYYY-MM-DDThh:mm:ss.ssssssZ For example: `"2019-05-21T10:04:02.123000-08:00"` or `"2019-05-21T10:04:02.123000Z"`.
yearmonthInterval	string	The string is in an ISO 8601 duration format that corresponds to a ym_iso_format specified for SQL function `to_yminterval`. PyYmM, where y is a digit sequence for the number of years and m is a digit sequence for the number of months. For example: `"P7Y8M"`. If the number of years or months is zero then it and its designator are omitted. Examples: `"P7Y"`, `"P8M"`. However, if there are zero years and zero months then the syntax is `"P0Y"`.

You can use json_serialize to convert binary JSON data to textual form (CLOB or VARCHAR2), or to transform textual JSON data by pretty-printing it or escaping non-ASCII Unicode characters in it. An important use case is serializing JSON data that is stored in a BLOB or JSON type column.

(You can use JSON data type only if database initialization parameter compatible is at least 20.)

A BLOB result is in the AL32UTF8 character set. But whatever the data type returned by json_serialize, the returned data represents textual JSON data.

Note:

You can use the JSON path-expression item method type() to determine the JSON-language type of any JSON scalar value.

See Also:

JSON_SERIALIZE in Oracle Database SQL Language Reference for information about Oracle SQL function json_serialize
RAWTOHEX in Oracle Database SQL Language Reference for information about SQL function rawtohex
TO_NUMBER in Oracle Database SQL Language Reference for information about SQL function to_number

Example 2-3 Using JSON_SERIALIZE To Convert JSON type or BLOB Data To Pretty-Printed Text with Ordered Object Members

This example serializes, orders object members, and pretty-prints the JSON purchase order that has 1600 as the value of field PONumber data, which is selected from column po_document of table j_purchaseorder. The return-value data type is VARCHAR2(4000) (the default return type).

Example 4-1 shows the creation of a table with a JSON type column. You can also use json_serialize to serialize BLOB data.

SELECT json_serialize(po_document PRETTY ORDERED)
  FROM j_purchaseorder po
  WHERE po.po_document.PONumber = 1600;

Example 2-4 Using JSON_SERIALIZE To Convert Non-ASCII Unicode Characters to ASCII Escape Codes

This example serializes an object that has a string field value with a non-ASCII character (€). It also orders the fields alphabetically.

SELECT json_serialize('{"price" : 20, "currency" : "€"}' ASCII ORDERED)
  FROM DUAL;

The query returns {"currency" : "\u20AC", "price" : 20}.

Related Topics

Parent topic: JSON Data Type

2.3.4 JSON Constructor, JSON_SCALAR, and JSON_SERIALIZE: Summary

Relations among JSON data type constructor JSON, Oracle SQL function json_scalar, and Oracle SQL function json_serialize are summarized.

Both constructor JSON and function json_scalar accept an instance of a SQL type other than JSON and return an instance of JSON data type.

The constructor accepts only textual JSON data as input: a VARCHAR2, CLOB, or BLOB instance. It raises an error for any other input data type.

Function json_scalar accepts an instance of any of several scalar SQL types as input. For VARCHAR2 or CLOB input it always returns a JSON-language string, as an instance of JSON type.

The value returned by the constructor can be any JSON value that is supported by Oracle, including values of the Oracle-specific scalar types: double, float, binary, date, timestamp, day-second interval, and year-month interval. If the constructor is used with keyword EXTENDED then the values can be derived from Oracle extended-object patterns in the textual JSON input.

The JSON value returned by json_scalar is always a scalar — same JSON-language types as for the constructor, except for the nonscalar types (object and array). For example, an instance of SQL type DOUBLE as input results in a JSON type instance representing a value of (Oracle-specific) JSON-language type double.

When Oracle SQL function json_serialize is applied to a JSON type instance, any non-standard Oracle scalar JSON value is returned as a standard JSON scalar value. But if json_serialize is used with keyword EXTENDED then values of Oracle-specific scalar JSON-language types can be serialized to Oracle extended-object patterns in the textual JSON output.

Table 2-4 summarizes the effects of using constructor JSON and SQL function json_scalar for various SQL values as JSON data, producing JSON type instances, and it shows the effect of serializing those instances.

The constructor parses the input, which must be textual JSON data (or else an error is raised). Function json_scalar converts its input SQL scalar value to a JSON-language scalar value. VARCHAR2 or CLOB input to json_scalar always results in a JSON string value (the input is not parsed as JSON data).

Except for the following facts, the result of serializing a value produced by the constructor is the same textual representation as was accepted by the constructor (but the textual SQL data type need not be the same, among VARCHAR2, CLOB, and BLOB):

The constructor accepts lax JSON syntax and json_serialize always returns strict syntax.
If any input JSON objects have duplicate field names then all but one of the field–value pairs is dropped by the constructor.
The order of field–value pairs in an object is not, in general, preserved: output order can differ from input order.
If the textual data to which the constructor is applied contains extended JSON constructs (JSON objects that specify non-standard scalar JSON values), then the resulting JSON type data can (with keyword EXTENDED) have some scalar values that result from translating those constructs to SQL scalar values. If json_serialize (with keyword EXTENDED) is applied to the resulting JSON type data then the result can include some extended JSON constructs that result from translating in the reverse direction.

The translations in these two directions are not, in general, inverse operations, however. They are exact inverses only for Oracle, not non-Oracle, extended JSON constructs. Because extended JSON constructs are translated to Oracle-specific JSON scalar values in JSON type, their serialization back to textual JSON data as extended JSON objects can be lossy when they are originally of a non-Oracle format.

Table 2-4 Effect of Constructor JSON and Oracle SQL Function JSON_SCALAR: Examples

Input SQL Value	SQL Type	JSON Value from JSON Constructor	JSON Scalar Value from JSON_SCALAR
`{a:1}`	`VARCHAR2`	JSON object with field `a` and value `1` `json_serialize` result: `{"a":1}`	JSON string containing the text `{"a":1}` `json_serialize` result: `"{\"a\":1}"` (escaped double-quote characters)
`[1,2,3]`	`VARCHAR2`	JSON array with elements `1`, `2`, `3` `json_serialize` result: `[1,2,3]`	JSON string containing the text `[1,2,3]` `json_serialize` result: `"[1,2,3]"`
`TRUE` (case-insensitive)	`BOOLEAN`	JSON Boolean value `true` `json_serialize` result: `true`	Same as `JSON` constructor.
`true`	`VARCHAR2`	JSON Boolean value `true` `json_serialize` result: `true`	JSON string containing the text `true` `json_serialize` result: `"true"`
`null`	`VARCHAR2`	JSON value `null` `json_serialize` result: `null`	JSON string containing the text `null` `json_serialize` result: `"null"`
`NULL`^Foot 1	`VARCHAR2`	SQL `NULL` (`JSON` type) — not JSON value `null` `json_serialize` result: SQL `NULL`	SQL `NULL` (`JSON` type) — not JSON value `null` `json_serialize` result: SQL `NULL`
`"city"`	`VARCHAR2`	JSON string containing the text `city` `json_serialize` result: `"city"`	JSON string containing the text `"city"` (including double-quote characters) `json_serialize` result: `"\"city\""` (escaped double-quote characters)
`city`	`VARCHAR2`	Error — input is not valid JSON data (there is no JSON scalar value `city`)	JSON string containing the text `city` `json_serialize` result: `"city"`
`{"$numberDouble" : "1E300"}` or `{"$numberDouble" : 1E300}` (An extended JSON object.)	`VARCHAR2`	JSON scalar of type double	A JSON string with the same content as the input `VARCHAR2` value
`{"$numberDecimal" : "1E300"}` or `{"$numberDecimal" : 1E300}` (An extended JSON object.)	`VARCHAR2`	JSON scalar of type number, tagged internally as having been derived from a `$numberDecimal` extended object	A JSON string with the same content as the input `VARCHAR2` value
`{"$oid" : "deadbeefcafe0123456789ab"}` or `{"$rawid" : "deadbeefcafe0123456789ab"}` (An extended JSON object.)	`VARCHAR2`	JSON scalar of type binary, tagged internally as having been derived from a `$rawid` or `$oid` extended object	A JSON string with the same content as the input `VARCHAR2` value
`{"$date" : "2020-11-24T12:34:56"}` or `{"$oracleDate" : "2020-11-24T12:34:56"}` (An extended JSON object.)	`VARCHAR2`	JSON scalar of type date, tagged internally as having been derived from an `$oracleDate` or `$date` extended object	A JSON string with the same content as the input `VARCHAR2` value
`3.14`	`VARCHAR2`	JSON number `3.14` `json_serialize` result: `3.14`	JSON string containing the text `3.14` `json_serialize` result: `"3.14"`
`3.14`	`NUMBER`	Error — not textual JSON data (SQL types other than `VARCHAR2`, `CLOB`, and `BLOB` are not supported)	JSON number value `3.14` `json_serialize` result: `3.14`
`3.14`	`BINARY_DOUBLE`	Error — not textual JSON data (SQL types other than `VARCHAR2`, `CLOB`, and `BLOB` are not supported)	JSON double value `3.14` (Oracle JSON language extension) `json_serialize` result: `3.14`
`3.14`	`NUMBER`, tagged internally as having been derived from a `$numberDecimal` extended object	JSON scalar of type number, tagged internally as having been derived from a `$numberDecimal` extended object	A JSON string with the same content as the original extended object
A `RAW` value	`RAW`, tagged internally as having been derived from a `$rawid` or `$oid` extended object	JSON scalar of type binary, tagged internally as having been derived from a `$rawid` or `$oid` extended object	A JSON string with the same content as the original extended object
SQL date value from evaluating `to_date('20.07.1974')`	`DATE`	Error — not textual JSON data	JSON date value (Oracle JSON language extension) `json_serialize` result: ISO 8601 string `"1974-07-20T00:00:00"` (UTC date — input format is ignored)
SQL timestamp value from evaluating `to_timestamp('2019-05-23 11:31:04.123', 'YYYY-MM-DD HH24:MI:SS.FF')`	`TIMESTAMP`	Error — not textual JSON data	JSON timestamp value (Oracle JSON language extension) `json_serialize` result: ISO 8601 string `"2019-05-23T11:31:04.123000"`
SQL timestamp value from evaluating `to_timestamp_tz('2019-05-23 11:31:04.123 -8', 'YYYY-MM-DD HH24:MI:SS.FF TZH')`	`TIMESTAMP WITH TIMEZONE`	Error — not textual JSON data	JSON timestamp with time zone value (Oracle JSON language extension) `json_serialize` result: ISO 8601 string `"2019-05-23T11:31.03.123000-08:00"`

^Footnote 1This is the SQL NULL value for type VARCHAR2, not a SQL string with characters NULL.

Related Topics

See Also:

Oracle Database SQL Language Reference in Oracle Database SQL Language Reference
Oracle Database SQL Language Reference in Oracle Database SQL Language Reference
Oracle Database SQL Language Reference in Oracle Database SQL Language Reference

Parent topic: JSON Data Type

2.3.5 Textual JSON Objects That Represent Extended Scalar Values

Native binary JSON data (OSON format) extends the JSON language by adding scalar types, such as date, that correspond to SQL types and are not part of the JSON standard. Oracle Database also supports the use of textual JSON objects that represent JSON scalar values, including such nonstandard values.

When you create native binary JSON data from textual JSON data that contains such extended objects, they can optionally be replaced with corresponding (native binary) JSON scalar values.

An example of an extended object is {"$numberDecimal":31}. It represents a JSON scalar value of the nonstandard type decimal number, and when interpreted as such it is replaced by a decimal number in native binary format.

For example, when you use the JSON data type constructor, JSON, if you use keyword EXTENDED then recognized extended objects in the textual input are replaced with corresponding scalar values in the native binary JSON result. If you do not include keyword EXTENDED then no such replacement occurs; the textual extended JSON objects are simply converted as-is to JSON objects in the native binary format.

In the opposite direction, when you use Oracle SQL function json_serialize to serialize binary JSON data as textual JSON data (VARCHAR2, CLOB, or BLOB), you can use keyword EXTENDED to replace (native binary) JSON scalar values with corresponding textual extended JSON objects.

Note:

If the database you use is an Oracle Autonomous Database then you can use PL/SQL procedure DBMS_CLOUD.copy_collection to create a JSON document collection from a file of JSON data such as that produced by common NoSQL databases, including Oracle NoSQL Database.

If you use ejson as the value of the type parameter of the procedure, then recognized extended JSON objects in the input file are replaced with corresponding scalar values in the resulting native binary JSON collection. In the other direction, you can use function json_serialize with keyword EXTENDED to replace scalar values with extended JSON objects in the resulting textual JSON data.

These are the two main use cases for extended objects:

Exchange (import/export):
- Ingest existing JSON data (from somewhere) that contains extended objects.
- Serialize native binary JSON data as textual JSON data with extended objects, for some use outside the database.
Inspection of native binary JSON data: see what you have by looking at corresponding extended objects.

For exchange purposes, you can ingest JSON data from a file produced by common NoSQL databases, including Oracle NoSQL Database, converting extended objects to native binary JSON scalars. In the other direction, you can export native binary JSON data as textual data, replacing Oracle-specific scalar JSON values with corresponding textual extended JSON objects.

As an example of inspection, consider an object such as {"dob" : "2000-01-02T00:00:00"} as the result of serializing native JSON data. Is "2000-01-02T00:00:00" the result of serializing a native binary value of type date, or is the native binary value just a string? Using json_serialize with keyword EXTENDED lets you know.

The mapping of extended object fields to scalar JSON types is, in general, many-to-one: more than one kind of extended JSON object can be mapped to a given scalar value. For example, the extended JSON objects {"$numberDecimal":"31"} and {"$numberLong:"31"} are both translated as the value 31 of JSON-language scalar type number, and item method type() returns "number" for each of those JSON scalars.

Item method type() reports the JSON-language scalar type of its targeted value (as a JSON string). Some scalar values are distinguishable internally, even when they have the same scalar type. This generally allows function json_serialize (with keyword EXTENDED) to reconstruct the original extended JSON object. Such scalar values are distinguished internally either by using different SQL types to implement them or by tagging them with the kind of extended JSON object from which they were derived.

When json_serialize reconstructs the original extended JSON object the result is not always textually identical to the original, but it is always semantically equivalent. For example, {"$numberDecimal":"31"} and {"$numberDecimal":31} are semantically equivalent, even though the field values differ in type (string and number). They are translated to the same internal value, and each is tagged as being derived from a $numberDecimal extended object (same tag). But when serialized, the result for both is {"$numberDecimal":31}. Oracle always uses the most directly relevant type for the field value, which in this case is the JSON-language value 31, of scalar type number.

Table 2-5 presents correspondences among the various types used. It maps across (1) types of extended objects used as input, (2) types reported by item method type(), (3) SQL types used internally, (4) standard JSON-language types used as output by function json_serialize, and (5) types of extended objects output by json_serialize when keyword EXTENDED is specified.

Table 2-5 Extended JSON Object Type Relations

^Footnote 2The string values are interpreted case-insensitively. For example, "NAN" "nan", and "nAn" are accepted and equivalent, and similarly "INF", "inFinity", and "iNf". Infinitely large ("Infinity" or "Inf") and small ("-Infinity" or "-Inf") numbers are accepted with either the full word or the abbreviation.

^Footnote 3On output, only these string values are used — no full-word Infinity or letter-case variants.

Related Topics

Parent topic: JSON Data Type

2.3.6 Comparison and Sorting of JSON Data Type Values

The canonical sort order for values of SQL data type JSON is described. It is used to compare all JSON values.

You can directly compare or sort values of JSON data type of any kind — whether scalar, object, or array. This means you can use JSON type directly in a WHERE clause, an ORDER BY clause, or a GROUP BY clause. The canonical sort order is defined across all JSON-type values, including scalar values derived from Oracle extended-object patterns in textual JSON input.

Note:

When comparing values of JSON data type in SQL, the size of the values being compared, as encoded for SQL comparison, must be less than 32K bytes. Otherwise, an error is raised. In practice, this SQL encoded-for-comparison size is roughly the size of a textual representation of the same JSON data.

For example, in this query the encoded sizes of fields dept and name must each be less than 32K:

SELECT * 
  FROM emp t
  WHERE t.data.dept = 'SALES' ORDER BY t.data.name

This limit applies to SQL clauses ORDER BY and GROUP BY, as well as to the use of SQL-value comparison operators (such as > in a WHERE clause).

More precisely, the limit applies only to comparison and sorting done by SQL itself. It does not apply to comparison or sorting done within the JSON language. That is, there's no size limit for comparison or sorting done by a SQL operator for JSON, such as json_transform or json_exists. In particular, the limit doesn't apply to comparisons made in SQL/JSON path expressions.

The JSON-type sort (comparison) order is as follows:

A scalar value sorts before a nonscalar value (after, with keyword DESC).
An object sorts before an array (after, with keyword DESC).
Two arrays are sorted by comparing their elements, in order. When two corresponding elements are unequal, the sort order of those elements determines the order of the two arrays. For example, with ascending sort order [4, 2, 5] sorts before [4, 2, 9] because 5 sorts before 9.

If all elements of one array are equal to the corresponding elements of a longer array, the shorter array sorts before the longer one. For example, with ascending sort order [4, 2] sorts before [4, 2, 5], but it sorts after [4, 1, 5].
Two objects are sorted first by field name, then by field value, as follows:
1. The members of each object are ordered by field name.
  
  Field names are compared as JSON string values, which uses the VARCHAR2 collation with binary ordering as represented in the AL32UTF8 character set.
2. Members of the sorted objects (from step 1) are compared, in order:
  - When two corresponding field names are different, the object with the field name that sorts first is sorted before the other object (after, with keyword DESC).
  - When two corresponding field names are the same, the field values are compared, according to the JSON-type sort order. (That is, field values are compared recursively.) The order of the two objects being compared follows that of their field values.
Two scalars of different type families are sorted in this ascending order by family — so, for example, a number sorts before a string. (For descending sort the order is reversed.)
1. null
2. Numeric (number, double, float)
3. string
4. Nonidentifier binary (e.g., images)
5. Identifier binary (e.g., values from extended objects with field $oid or $rawid)
6. boolean
7. Date and time points (date, timestamp, or timestamp with time zone)
8. yearmonthInterval
9. daysecondInterval
There are two separate families for both date-time interval values and binary values, because the values need to be compared and sorted separately. Different months can have a different number of days. Binary values that are used as identifiers are typically tested for equality; equality testing, even when possible, is typically not useful for nonidentifier binary values.
Two scalars of the same type family are sorted by the sort order defined for that family. For example, with ascending sort order, 100 sorts before 200.0 regardless of the numeric types used, and "cat" sorts before "dog" regardless of the character set used.

The scalar JSON comparison used is the collation for the corresponding SQL scalar type, except that a JSON string comparison uses the VARCHAR2 collation with binary ordering as represented in the AL32UTF8 character set. For boolean values, false sorts before true (after, with keyword DESC).

You can compare any values of JSON type for purposes of sorting, such as is done by ORDER BY. But comparison for other purposes, for example in a comparison filter condition, is more limited.

Apart from sorting, you can compare any values that are in the same type family in any way. Values from different type families are always unequal: comparison for equality (==) yields false and comparison for inequality (!=, <>) yields true). Comparisons <, <=, >=, and > are meaningful and useful only within the same family; if used with values from different families then the comparison condition returns false. For example, a JSON object, number, or boolean is neither greater than nor less than a JSON array, string, or date.

Tip:

For example instead of this:

SELECT data FROM customers c
  ORDER BY c.data.revenue;

Use this:

SELECT data FROM customers c
  ORDER BY json_scalar(c.data.revenue);

You can use item method type() to help you identify the type family of a JSON value, which makes it useful for purposes of comparison or indexing. However, it provides only a rough guide for this, because it generally reports only on the SQL data type from which the JSON value was derived, or to which the JSON value can be mapped.

null type family: type() returns "null".
Numeric type family: type() returns different type names for different kinds of numeric value:
- "double", for a JSON value (a number) that corresponds to a SQL BINARY_DOUBLE value. This includes, for example, values that were derived from an extended object with $numberDouble.
- "float", for a JSON value (a number) that corresponds to a SQL BINARY_FLOAT value. This includes, for example, values that were derived from an extended object with $numberFloat.
- "number", for a JSON value (a number) that was derived from either (1) a textual JSON number or a string numeral (corresponding to the standard JSON-language number type) or (2) an extended object with $numberInt, $numberDecimal, or $numberLong.
string type family: type() returns "string".
Binary type families: type() returns "binary" for both the identifier and nonidentifier binary families, that is, a value that corresponds to a SQL RAW value. type() cannot distinguish values of these two families.
boolean type family: type() returns "boolean".
Date and time point family returns different type names for different kinds:
- "date" for a value that corresponds to a SQL DATE value. This includes, for example, values that were derived from an extended object with $oracleDate.
- "timestamp" for a value that corresponds to a SQL TIMESTAMP value. This includes, for example, values that were derived from an extended object with $oracleTimestamp.
- "timestamp with time zone" for a value that corresponds to a SQL TIMESTAMP WITH TIME ZONE value. This includes, for example, values that were derived from an extended object with $date or $oracleTimestampTZ. (A $date field has a timestamp-with-timezone value, because it allows fractional seconds, and the value is given for Coordinated Universal Time (UTC).)
yearMonthInterval type family: type() returns "yearmonthInterval" for a value that corresponds to a SQL INTERVAL YEAR TO MONTH value. This includes, for example, values that were derived from an extended object with $intervalYearMonth.
daysecondInterval type family: type() returns "daysecondInterval" for a value that corresponds to a SQL INTERVAL DAY TO SECOND value. This includes, for example, values that were derived from an extended object with $intervalDaySecond.

Related Topics

See Also:

Data Type Comparison Rules in Oracle Database SQL Language Reference for information about how Oracle Database compares values within each data type

Parent topic: JSON Data Type

2.4 Oracle Database Support for JSON

Oracle Database support for JavaScript Object Notation (JSON) is designed to provide the best fit between the worlds of relational storage and querying JSON data, allowing relational and JSON queries to work well together. Oracle SQL/JSON support is closely aligned with the JSON support in the SQL Standard.

Oracle Database supports the JSON format as specified in ECMAScript edition 5.1.

Support for RFC 8259: JSON Scalars
Starting with Release 21c, Oracle Database can support IETF RFC 8259, which allows a JSON document to contain only a JSON scalar value at top level. This support also means that functions that return JSON data can return scalar JSON values.

See Also:

ISO/IEC 9075-2:2016, Information technology—Database languages—SQL—Part 2: Foundation (SQL/Foundation)
ISO/IEC TR 19075–6
Oracle Database SQL Language Reference
JSON.org and JSON5
ECMA International
ECMA 262 and ECMA 262, 5.1 Edition for the ECMAScript Language Specifications (JavaScript)

Parent topic: JSON in Oracle Database

2.4.1 Support for RFC 8259: JSON Scalars

Starting with Release 21c, Oracle Database can support IETF RFC 8259, which allows a JSON document to contain only a JSON scalar value at top level. This support also means that functions that return JSON data can return scalar JSON values.

For this support, database initialization parameter compatible must be 20 or greater.

In database releases prior to 21c only IETF RFC 4627 was supported. It allows only a JSON object or array, not a scalar, at the top level of a JSON document. RFC 8259 support includes RFC 4627 support (and RFC 7159 support).

If parameter compatible is 20 or greater then JSON data, regardless of how it is stored, supports RFC 8259 by default. But for a given JSON column you can use an is json check constraint to exclude the insertion of documents there that have top-level JSON scalars (that is, support only RFC 4627, not RFC 8259), by specifying the new is json keywords DISALLOW SCALARS.

With parameter compatible 20 or greater you can also use keywords DISALLOW SCALARS with SQL/JSON function json_query (or with a json_table column that has json_query semantics) to specify that the return value must be a JSON object or array. Without these keywords a JSON scalar can be returned.

If parameter compatible is 20 or greater you can also use SQL data type JSON, its constructor JSON, and Oracle SQL function json_scalar. If compatible is less than 20 then an error is raised when you try to use them.

If compatible is 20 or greater you can nevertheless restrict some JSON data to not allow top-level scalars, by using keywords DISALLOW SCALARS. For example, you can use an is json check constraint with DISALLOW SCALARS to prevent the insertion of documents that have a top-level scalar JSON value.

WARNING:

If you change the value of parameter compatible to 20 or greater then you cannot later return it to a lower value.

Parent topic: Oracle Database Support for JSON

Extended Object Type (Input)	Oracle JSON Scalar Type (Reported by type())	SQL Scalar Type	Standard JSON Scalar Type (Output)	Extended Object Type (Output)
`$numberDouble` with value a JSON number, a string representing the number, or one of these strings: `"Infinity"`, `"-Infinity"`, `"Inf"`, `"-Inf"`, `"Nan"`^Foot 2	double	`BINARY_DOUBLE`	number	`$numberDouble` with value a JSON number or one of these strings: `"Inf"`, `"-Inf"`, `"Nan"`^Foot 3
`$numberFloat` with value the same as for `$numberDouble`	float	`BINARY_FLOAT`	number	`$numberFloat` with value the same as for `$numberDouble`
`$numberDecimal` with value the same as for `$numberDouble`	number	`NUMBER`	number	`$numberDecimal` with value the same as for `$numberDouble`
`$numberInt` with value a signed 32-bit integer or a string representing the number	number	`NUMBER`	number	`$numberInt` with value the same as for `$numberDouble`
`$numberLong` with value a JSON number or a string representing the number	number	`NUMBER`	number	`$numberLong` with value the same as for `$numberDouble`
`$binary` with value one of these: a string of base-64 characters An object with fields `base64` and `subType`, whose values are a string of base-64 characters and the number `0` (arbitrary binary) or `4` (UUID), respectively When the value is a string of base-64 characters, the extended object can also have field `$subtype` with value 0 or 4, expressed as a one-byte integer (0-255) or a 2-character hexadecimal string. representing such an integer	binary	`BLOB` or `RAW`	string Conversion is equivalent to the use of SQL function `rawtohex`.	One of the following: `$binary` with value a string of base-64 characters `$rawid` with value a string of 32 hexadecimal characters, if input had a `subType` value of `4` (UUID)
`$oid` with value a string of 24 hexadecimal characters	binary	`RAW(12)`	string Conversion is equivalent to the use of SQL function `rawtohex`.	`$rawid` with value a string of 24 hexadecimal characters
`$rawhex` with value a string with an even number of hexadecimal characters	binary	`RAW`	string Conversion is equivalent to the use of SQL function `rawtohex`.	`$binary` with value a string of base-64 characters, right-padded with `=` characters
`$rawid` with value a string of 24 or 32 hexadecimal characters	binary	`RAW`	string Conversion is equivalent to the use of SQL function `rawtohex`.	`$rawid`
`$oracleDate` with value an ISO 8601 date string	date	`DATE`	string	`$oracleDate` with value an ISO 8601 date string
`$oracleTimestamp` with value an ISO 8601 timestamp string	timestamp	`TIMESTAMP`	string	`$oracleTimestamp` with value an ISO 8601 timestamp string
`$oracleTimestampTZ` with value an ISO 8601 timestamp string with a numeric time zone offset or with `Z`	timestamp with time zone	`TIMESTAMP WITH TIME ZONE`	string	`$oracleTimestampTZ` with value an ISO 8601 timestamp string with a numeric time zone offset or with `Z`
`$date` with value one of the following: An integer millisecond count since January 1, 1990 An ISO 8601 timestamp string An object with field `numberLong` with value an integer millisecond count since January 1, 1990	timestamp with time zone	`TIMESTAMP WITH TIME ZONE`	string	`$oracleTimestampTZ` with value an ISO 8601 timestamp string with a numeric time zone offset or with `Z`
`$intervalDaySecond` with value an ISO 8601 interval string as specified for SQL function `to_dsinterval`	daysecondInterval	`INTERVAL DAY TO SECOND`	string	`$intervalDaySecond` with value an ISO 8601 interval string as specified for SQL function `to_dsinterval`
`$intervalYearMonth` with value an ISO 8601 interval string as specified for SQL function `to_yminterval`	yearmonthInterval	`INTERVAL YEAR TO MONTH`	string	`$intervalYearMonth` with value an ISO 8601 interval string as specified for SQL function `to_yminterval`