json_query selects one or more values from JSON data and returns a string (
BLOB instance) that represents the JSON values. You can thus use
json_query to retrieve fragments of a JSON document.
The first argument to
json_query is a SQL expression that returns an instance of a scalar SQL data type (that is, not an object or collection data type). It can be of data type
BLOB. It can be a table or view column value, a PL/SQL variable, or a bind variable with proper casting. The result of evaluating the SQL expression is used as the context item for evaluating the path expression.
The second argument to
json_query is a SQL/JSON path expression followed by optional clauses
ON ERROR, and
ON EMPTY. The path expression can target any number of JSON values.
RETURNING clause you can specify data type
BLOB result is in the AL32UTF8 character set. (
VARCHAR2 is the default.) The value returned always contains well-formed JSON data. This includes ensuring that non-ASCII characters in string values are escaped as needed. For example, an ASCII TAB character (Unicode character CHARACTER TABULATION, U+0009) is escaped as
FORMAT JSON are not needed (or available) for
json_query — JSON formatting is implicit for the return value.
The wrapper clause determines the form of the returned string value.
The error clause for
json_query can specify
EMPTY ON ERROR, which means that an empty array (
) is returned in case of error (no error is raised).
Example 17-1 shows an example of the use of SQL/JSON function
json_query with an array wrapper. For each document it returns a
VARCHAR2 value whose contents represent a JSON array with elements the phone types, in an unspecified order. For the document in Example 4-2 the phone types are
"Mobile", and the array returned is either
["Mobile", "Office"] or
Note that if path expression
$.ShippingInstructions.Phone.type were used in Example 17-1 it would give the same result. Because of SQL/JSON path-expression syntax relaxation,
[*].type is equivalent to
Oracle Database SQL Language Reference for information about
Example 17-1 Selecting JSON Values Using JSON_QUERY
SELECT json_query(po_document, '$.ShippingInstructions.Phone[*].type' WITH WRAPPER) FROM j_purchaseorder;
17.1 JSON_QUERY as JSON_TABLE
json_query can be viewed as a special case of function
Example 17-2 illustrates the equivalence: the two
SELECT statements have the same effect.
In addition to perhaps helping you understand
json_query better, this equivalence is important practically, because it means that you can use either function to get the same effect.
In particular, if you use
json_query more than once, or you use it in combination with
json_value (which can also be expressed using
json_table), to access the same data, then a single invocation of
json_table presents the advantage that the data is parsed only once.
Because of this, the optimizer often automatically rewrites multiple invocations of
json_query (any combination) to fewer invocations of
Example 17-2 JSON_QUERY Expressed Using JSON_TABLE
SELECT json_query(column, json_path RETURNING data_type array_wrapper error_hander ON ERROR) FROM table; SELECT jt.column_alias FROM table, json_table(column, '$' error_handler ON ERROR COLUMNS ("COLUMN_ALIAS" data_type FORMAT JSON array_wrapper PATH json_path)) AS "JT";