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Oracle® Call Interface Programmer's Guide
11g Release 1 (11.1)

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6 Describing Schema Metadata

This chapter discusses the use of the OCIDescribeAny() function to obtain information about schema elements.

This chapter contains these topics:

Using OCIDescribeAny()

The OCIDescribeAny() function enables you to perform an explicit describe of the following schema objects and their subschema objects:

  • tables and views

  • synonyms

  • procedures

  • functions

  • packages

  • sequences

  • collections

  • types

  • schemas

  • databases

Information about other schema elements (function arguments, columns, type attributes, and type methods) is available through a describe of one of the preceding schema objects or an explicit describe of the subschema object.

When an application describes a table, it can then retrieve information about that table's columns. Additionally, OCIDescribeAny() can directly describe subschema objects such as columns of a table, packages of a function, or fields of a type if given the name of the subschema object.

The OCIDescribeAny() call requires a describe handle as one of its arguments. The describe handle must be previously allocated with a call to OCIHandleAlloc().

The information returned by OCIDescribeAny() is organized hierarchically like a tree, as shown in Figure 6-1:

Figure 6-1 OCIDescribeAny() Table Description

Description of Figure 6-1 follows
Description of "Figure 6-1 OCIDescribeAny() Table Description"

The describe handle returned by OCIDescribeAny() has an attribute, OCI_ATTR_PARAM, that points to such a description tree. Each node of the tree has attributes associated with that node, and attributes that are like recursive describe handles and point to subtrees containing further information. If all the attributes are homogenous, as in the case of elements of a column list, they are called parameters. The attributes associated with any node are returned by OCIAttrGet(), and the parameters are returned by OCIParamGet().

A call to OCIAttrGet() on the describe handle for the table returns a handle to the column-list information. An application can then use OCIParamGet() to retrieve the handle to the column description of a particular column in the column-list. The handle to the column descriptor can be passed to OCIAttrGet() to get further information about the column, such as the name and datatype.

After a SQL statement is executed, information about the select-list is available as an attribute of the statement handle. No explicit describe call is needed. To retrieve information about select-list items from the statement handle, the application must call OCIParamGet() once for each position in the select-list to allocate a parameter descriptor for that position.

Note:

No subsequent OCIAttrGet() or OCIParamGet() call requires extra round trips, as all the description is cached on the client side by OCIDescribeAny().

Limitations on OCIDescribeAny()

The OCIDescribeAny() call limits information returned to the basic information and stops expanding a node if it amounts to another describe. For example, if a table column is of an object type, then the OCI does not return a subtree describing the type since this information can be obtained by another describe.

The table name is not returned by OCIDescribeAny() or the implicit use of OCIStmtExecute(). Sometimes a column is not associated with a table. In most cases, the table is already known.

Notes on Types and Attributes

When performing describe operations, you should be aware of the following:

Datatype Codes

OCI_ATTR_TYPECODE returns typecodes which represent the types supplied by the user when a new type is created using the CREATE TYPE statement. These typecodes are of the enumerated type OCITypeCode, and are represented by OCI_TYPECODE constants. Internal PL/SQL type (boolean) is not supported.

OCI_ATTR_DATA_TYPE returns typecodes which represent the datatypes stored in database columns. These are similar to the describe values returned by previous versions of Oracle. These values are represented by SQLT constants (ub2 values). BOOLEAN types return SQLT_BOL.

See Also:

"Typecodes" for more information about typecodes, such as the OCI_TYPCODE values returned in the OCI_ATTR_TYPECODE attribute and the SQLT typecodes returned in the OCI_ATTR_DATA_TYPE attribute

Describing Types

In order to describe type objects, it is necessary to initialize the OCI process in object mode:

/* Initialize the OCI Process */
 if (OCIEnvCreate((OCIEnv **) &envhp, (ub4) OCI_OBJECT, (voivoid *) 0,
                  (void * (*)(void *,size_t)) 0,
                  (void * (*)(void *, void *, size_t)) 0,
                  (void (*)(void *, void *)) 0, (size_t) 0, (void **) 0))
 {
   printf("FAILED: OCIEnvCreate()\n");
   return OCI_ERROR;
 }

Note on Implicit and Explicit Describes

The column attribute OCI_ATTR_PRECISION can be returned using an implicit describe with OCIStmtExecute() and an explicit describe with OCIDescribeAny(). When using an implicit describe, the precision should be set to sb2. When using an explicit describe, the precision should be set to ub1 for a placeholder. This is necessary to match the datatype of precision in the dictionary.

Note on OCI_ATTR_LIST_ARGUMENTS

The OCI_ATTR_LIST_ARGUMENTS attribute for type methods represents second-level arguments for the method.

For example, given the following record my_type and the procedure my_proc which takes an argument of type my_type:

my_type record(a number, b char)
my_proc (my_input my_type)

the OCI_ATTR_LIST_ARGUMENTS attribute would apply to arguments a and b of the my_type record.

Parameter Attributes

A parameter is returned by OCIParamGet(). Parameters can describe different types of objects or information, and have attributes depending on the type of description they contain, or type-specific attributes. This section describes the attributes and handles that belong to different parameters.

Note that OCIDescribeAny() does support more than two name components, for example, schema.type.attr1.attr2.method1. Note that with more than one component, the first component is interpreted as the schema name (unless some other flag is set). There is a flag to specify that the object must be looked up under PUBLIC, that is, describe "a", where "a" can be either in the current schema or a public synonym.

If you do not know what the object type is, specify OCI_PTYPE_UNK. Otherwise an error is returned if the actual object type does not match the specified type.

Table 6-1 lists the attributes of all parameters:

Table 6-1 Attributes of All Parameters

Attribute Description Attribute Datatype

OCI_ATTR_OBJ_ID

Object or schema ID

ub4

OCI_ATTR_OBJ_NAME

Database name or object name in a schema

OraText *

OCI_ATTR_OBJ_SCHEMA

Schema name where the object is located

OraText *

OCI_ATTR_PTYPE

Type of information described by the parameter. Possible values:

OCI_PTYPE_TABLE - table

OCI_PTYPE_VIEW - view

OCI_PTYPE_PROC - procedure

OCI_PTYPE_FUNC - function

OCI_PTYPE_PKG - package

OCI_PTYPE_TYPE - type

OCI_PTYPE_TYPE_ATTR - attribute of a type

OCI_PTYPE_TYPE_COLL - collection type information

OCI_PTYPE_TYPE_METHOD - method of a type

OCI_PTYPE_SYN - synonym

OCI_PTYPE_SEQ - sequence

OCI_PTYPE_COL - column of a table or view

OCI_PTYPE_ARG - argument of a function or procedure

OCI_PTYPE_TYPE_ARG - argument of a type method

OCI_PTYPE_TYPE_RESULT - results of a method

OCI_PTYPE_LIST - column list for tables and views, argument list for functions and procedures, or subprogram list for packages.

OCI_PTYPE_SCHEMA - schema

OCI_PTYPE_DATABASE - database

OCI_PTYPE_UNK - unknown schema object

ub1 

OCI_ATTR_TIMESTAMP

The timestamp of the object on which the description is based in Oracle date format

ub1 *

The following sections list the attributes and handles specific to different types of parameters.

Table or View Parameters

Parameters for a table or view (type OCI_PTYPE_TABLE or OCI_PTYPE_VIEW) have the following type-specific attributes:

Table 6-2 Attributes of Tables or Views

Attribute Description Attribute Datatype

OCI_ATTR_OBJID

Object id

ub4

OCI_ATTR_NUM_COLS

Number of columns

ub2

OCI_ATTR_LIST_COLUMNS

Column list (type OCI_PTYPE_LIST)

OCIParam *

OCI_ATTR_REF_TDO

REF to the TDO of the base type in case of extent tables

OCIRef*

OCI_ATTR_IS_TEMPORARY

Indicates the table is temporary

ub1

OCI_ATTR_IS_TYPED

Indicates the table is typed

ub1

OCI_ATTR_DURATION

Duration of a temporary table. Values can be:

OCI_DURATION_SESSION - session

OCI_DURATION_TRANS - transaction

OCI_DURATION_NULL -table not temporary

OCIDuration

The following are additional attributes which belong to tables:

Table 6-3 Attributes Specific to Tables

Attribute Description Attribute Datatype

OCI_ATTR_RDBA

Data block address of the segment header

ub4

OCI_ATTR_TABLESPACE

Tablespace the table resides in

word

OCI_ATTR_CLUSTERED

Indicates the table is clustered

ub1

OCI_ATTR_PARTITIONED

Indicates the table is partitioned

ub1

OCI_ATTR_INDEX_ONLY

Indicates the table is index-only

ub1

Procedure, Function, Subprogram Attributes

When a parameter is for a procedure or function (type OCI_PTYPE_PROC or OCI_PTYPE_FUNC), it has the following type specific attributes:

Table 6-4 Attribute of Procedures or Functions

Attribute Description Attribute Datatype

OCI_ATTR_LIST_ARGUMENTS

Argument list. See "List Attributes".

void *

OCI_ATTR_IS_INVOKER_RIGHTS

Indicates the procedure or function has invoker's rights

ub1

The following attributes are defined only for package subprograms:

Table 6-5 Attributes Specific to Package Subprograms

Attribute Description Attribute Datatype

OCI_ATTR_NAME

Name of the procedure or function

OraText *

OCI_ATTR_OVERLOAD_ID

Overloading ID number (relevant in case the procedure or function is part of a package and is overloaded). Values returned may be different from direct query of a PL/SQL function or procedure.

ub2

Package Attributes

When a parameter is for a package (type OCI_PTYPE_PKG), it has the following type specific attributes:

Table 6-6 Attributes of Packages

Attribute Description Attribute Datatype

OCI_ATTR_LIST_SUBPROGRAMS

Subprogram list. See "List Attributes".

void *

OCI_ATTR_IS_INVOKER_RIGHTS

Is the package invoker's rights?

ub1

Type Attributes

When a parameter is for a type (type OCI_PTYPE_TYPE), it has the attributes listed in Table 6-7. These attributes are only valid if the application initialized the OCI process in OCI_OBJECT mode in a call to OCIInitialize().

Table 6-7 Attributes of Types

Attribute Description Attribute Datatype

OCI_ATTR_REF_TDO

Returns the in-memory REF of the type descriptor object for the type, if the column type is an object type. If space has not been reserved for the OCIRef, then it is allocated implicitly in the cache. The caller can then pin the TDO with OCIObjectPin().

OCIRef *

OCI_ATTR_TYPECODE

Typecode. See "Datatype Codes". Currently can be only OCI_TYPECODE_OBJECT or OCI_TYPECODE_NAMEDCOLLECTION.

OCITypeCode

OCI_ATTR_COLLECTION_TYPECODE

Typecode of collection if type is collection; invalid otherwise. See "Datatype Codes". Currently can be only OCI_TYPECODE_VARRAY or OCI_TYPECODE_TABLE. Error is returned if this attribute is queried for non-collection type.

OCITypeCode

OCI_ATTR_IS_INCOMPLETE_TYPE

Indicates this is an incomplete type

ub1

OCI_ATTR_IS_SYSTEM_TYPE

Indicates this is a system type

ub1

OCI_ATTR_IS_PREDEFINED_TYPE

Indicates this is a predefined type

ub1

OCI_ATTR_IS_TRANSIENT_TYPE

Indicates this is a transient type

ub1

OCI_ATTR_IS_SYSTEM_GENERATED_TYPE

Indicates this is a system-generated type

ub1

OCI_ATTR_HAS_NESTED_TABLE

This type contains a nested table attribute

ub1

OCI_ATTR_HAS_LOB

This type contains a LOB attribute

ub1

OCI_ATTR_HAS_FILE

This type contains a BFILE attribute

ub1

OCI_ATTR_COLLECTION_ELEMENT

Handle to collection element. See "Collection Attributes".

void *

OCI_ATTR_NUM_TYPE_ATTRS

Number of type attributes

ub2

OCI_ATTR_LIST_TYPE_ATTRS

List of type attributes. See "List Attributes".

void *

OCI_ATTR_NUM_TYPE_METHODS

Number of type methods

ub2

OCI_ATTR_LIST_TYPE_METHODS

List of type methods. See "List Attributes".

void *

OCI_ATTR_MAP_METHOD

Map method of type. See "Type Method Attributes".

void *

OCI_ATTR_ORDER_METHOD

Order method of type. See "Type Method Attributes".

void *

OCI_ATTR_IS_INVOKER_RIGHTS

Indicates the type has invoker's rights

ub1

OCI_ATTR_NAME

A pointer to a string which is the type attribute name

OraText *

OCI_ATTR_SCHEMA_NAME

A string with the schema name where the type has been created

OraText *

OCI_ATTR_IS_FINAL_TYPE

Indicates this is a final type

ub1

OCI_ATTR_IS_INSTANTIABLE_TYPE

Indicates this is an instantiable type

ub1

OCI_ATTR_IS_SUBTYPE

Indicates this is a subtype

ub1

OCI_ATTR_SUPERTYPE_SCHEMA_NAME

Name of the schema that contains the supertype

OraText *

OCI_ATTR_SUPERTYPE_NAME

Name of the supertype

OraText *

Type Attribute Attributes

When a parameter is for an attribute of a type (type OCI_PTYPE_TYPE_ATTR), it has the attributes listed in Table 6-8.

Table 6-8 Attributes of Type Attributes

Attribute Description Attribute Datatype

OCI_ATTR_DATA_SIZE

The maximum size of the type attribute. This length is returned in bytes and not characters for strings and raws. It returns 22 for NUMBERs.

ub2

OCI_ATTR_TYPECODE

Typecode. See "Datatype Codes".

OCITypeCode

OCI_ATTR_DATA_TYPE

The datatype of the type attribute. See "Datatype Codes".

ub2

OCI_ATTR_NAME

A pointer to a string which is the type attribute name

OraText *

OCI_ATTR_PRECISION

The precision of numeric type attributes. If the precision is nonzero and scale is -127, then it is a FLOAT, else it is a NUMBER(precision, scale). For the case when precision is 0, NUMBER(precision, scale) can be represented simply as NUMBER.

ub1 for explicit describe
sb2 for implicit describe

OCI_ATTR_SCALE

The scale of numeric type attributes. If the precision is nonzero and scale is -127, then it is a FLOAT, else it is a NUMBER(precision, scale). For the case when precision is 0, NUMBER(precision, scale) can be represented simply as NUMBER.

sb1

OCI_ATTR_TYPE_NAME

A string which is the type name. The returned value will contain the type name if the datatype is SQLT_NTY or SQLT_REF. If the datatype is SQLT_NTY, the name of the named datatype's type is returned. If the datatype is SQLT_REF, the type name of the named datatype pointed to by the REF is returned

OraText *

OCI_ATTR_SCHEMA_NAME

A string with the schema name under which the type has been created

OraText *

OCI_ATTR_REF_TDO

Returns the in-memory REF of the TDO for the type, if the column type is an object type. If space has not been reserved for the OCIRef, then it is allocated implicitly in the cache. The caller can then pin the TDO with OCIObjectPin().

OCIRef *

OCI_ATTR_CHARSET_ID

The character set id, if the type attribute is of a string/character type

ub2

OCI_ATTR_CHARSET_FORM

The character set form, if the type attribute is of a string/character type

ub1

OCI_ATTR_FSPRECISION

The fractional seconds precision of a datetime or interval.

ub1

OCI_ATTR_LFPRECISION

The leading field precision of an interval.

ub1

Type Method Attributes

When a parameter is for a method of a type (type OCI_PTYPE_TYPE_METHOD), it has the attributes listed in Table 6-9.

Table 6-9 Attributes of Type Methods

Attribute Description Attribute Datatype

OCI_ATTR_NAME

Name of method (procedure or function)

OraText *

OCI_ATTR_ENCAPSULATION

Encapsulation level of the method (either OCI_TYPEENCAP_PRIVATE or OCI_TYPEENCAP_PUBLIC)

OCITypeEncap

OCI_ATTR_LIST_ARGUMENTS

Argument list. See "Note on OCI_ATTR_LIST_ARGUMENTS", and "List Attributes".

void *

OCI_ATTR_IS_CONSTRUCTOR

Indicates method is a constructor

ub1

OCI_ATTR_IS_DESTRUCTOR

Indicates method is a destructor

ub1

OCI_ATTR_IS_OPERATOR

Indicates method is an operator

ub1

OCI_ATTR_IS_SELFISH

Indicates method is selfish

ub1

OCI_ATTR_IS_MAP

Indicates method is a map method

ub1

OCI_ATTR_IS_ORDER

Indicates method is an order method

ub1

OCI_ATTR_IS_RNDS

Indicates "Read No Data State" is set for method

ub1

OCI_ATTR_IS_RNPS

Indicates "Read No Process State" is set for method

ub1

OCI_ATTR_IS_WNDS

Indicates "Write No Data State" is set for method

ub1

OCI_ATTR_IS_WNPS

Indicates "Write No Process State" is set for method

ub1

OCI_ATTR_IS_FINAL_METHOD

Indicates this is a final method

ub1

OCI_ATTR_IS_INSTANTIABLE_METHOD

Indicates this is an instantiable method

ub1

OCI_ATTR_IS_OVERRIDING_METHOD

Indicates this is an overriding method

ub1

Collection Attributes

When a parameter is for a collection type (type OCI_PTYPE_COLL), it has the attributes listed in Table 6-10.

Table 6-10 Attributes of Collection Types

Attribute Description Attribute Datatype

OCI_ATTR_DATA_SIZE

The maximum size of the type attribute. This length is returned in bytes and not characters for strings and raws. It returns 22 for NUMBERs.

ub2

OCI_ATTR_TYPECODE

Typecode. See "Datatype Codes".

OCITypeCode

OCI_ATTR_DATA_TYPE

The datatype of the type attribute. See "Datatype Codes".

ub2

OCI_ATTR_NUM_ELEMS

The number of elements in an array. It is only valid for collections that are arrays

ub4

OCI_ATTR_NAME

A pointer to a string which is the type attribute name

OraText *

OCI_ATTR_PRECISION

The precision of numeric type attributes. If the precision is nonzero and scale is -127, then it is a FLOAT, else it is a NUMBER(precision, scale). For the case when precision is 0, NUMBER(precision, scale) can be represented simply as NUMBER.

ub1 for explicit describe
sb2 for implicit describe

OCI_ATTR_SCALE

The scale of numeric type attributes. If the precision is nonzero and scale is -127, then it is a FLOAT, else it is a NUMBER(precision, scale). For the case when precision is 0, NUMBER(precision, scale) can be represented simply as NUMBER.

sb1

OCI_ATTR_TYPE_NAME

A string which is the type name. The returned value will contain the type name if the datatype is SQLT_NTY or SQLT_REF. If the datatype is SQLT_NTY, the name of the named datatype's type is returned. If the datatype is SQLT_REF, the type name of the named datatype pointed to by the REF is returned

OraText *

OCI_ATTR_SCHEMA_NAME

A string with the schema name under which the type has been created

OraText *

OCI_ATTR_REF_TDO

Returns the in-memory REF of the TDO for the type, if the column type is an object type. If space has not been reserved for the OCIRef, then it is allocated implicitly in the cache. The caller can then pin the TDO with OCIObjectPin().

OCIRef *

OCI_ATTR_CHARSET_ID

The character set id, if the type attribute is of a string/character type

ub2

OCI_ATTR_CHARSET_FORM

The character set form, if the type attribute is of a string/character type

ub1

Synonym Attributes

When a parameter is for a synonym (type OCI_PTYPE_SYN), it has the attributes listed in Table 6-11.

Table 6-11 Attributes of Synonyms

Attribute Description Attribute Datatype

OCI_ATTR_OBJID

Object id

ub4

OCI_ATTR_SCHEMA_NAME

A string containing the schema name of the synonym translation

OraText *

OCI_ATTR_NAME

A NULL-terminated string containing the object name of the synonym translation

OraText *

OCI_ATTR_LINK

A NULL-terminated string containing the database link name of the synonym translation

OraText *

Sequence Attributes

When a parameter is for a sequence (type OCI_PTYPE_SEQ), it has the attributes listed in Table 6-12.

Table 6-12 Attributes of Sequences

Attribute Description Attribute Datatype

OCI_ATTR_OBJID

Object id

ub4

OCI_ATTR_MIN

Minimum value (in Oracle NUMBER format)

ub1 *

OCI_ATTR_MAX

Maximum value (in Oracle NUMBER format)

ub1 *

OCI_ATTR_INCR

Increment (in Oracle NUMBER format)

ub1 *

OCI_ATTR_CACHE

Number of sequence numbers cached; zero if the sequence is not a cached sequence (in Oracle NUMBER format)

ub1 *

OCI_ATTR_ORDER

Whether the sequence is ordered

ub1

OCI_ATTR_HW_MARK

High-water mark (in NUMBER format)

ub1 *

Column Attributes

Note:

For BINARY_FLOAT and BINARY_DOUBLE:

If OCIDescribeAny() is used to retrieve the column datatype (OCI_ATTR_DATA_TYPE) for BINARY_FLOAT or BINARY_DOUBLE columns in a table, it returns the internal datatype code.

The SQLT codes corresponding to the internal datatype codes for BINARY_FLOAT and BINARY_DOUBLE are SQLT_IBFLOAT and SQLT_IBDOUBLE.

When a parameter is for a column of a table or view (type OCI_PTYPE_COL), it has the attributes listed in Table 6-13.

Table 6-13 Attributes of Columns of Tables or Views

Attribute Description Attribute Datatype

OCI_ATTR_CHAR_USED

Returns the type of length semantics of the column. 0 means byte-length semantics and 1 means character-length semantics. See "Character Length Semantics Support in Describing".

ub1

OCI_ATTR_CHAR_SIZE

Returns the column character length which is the number of characters allowed in the column. It is the counterpart of OCI_ATTR_DATA_SIZE which gets the byte length. See "Character Length Semantics Support in Describing".

ub2

OCI_ATTR_DATA_SIZE

The maximum size of the column. This length is returned in bytes and not characters for strings and raws. It returns 22 for NUMBERs.

ub2

OCI_ATTR_DATA_TYPE

The datatype of the column. See "Datatype Codes".

ub2

OCI_ATTR_NAME

A pointer to a string which is the column name

OraText *

OCI_ATTR_PRECISION

The precision of numeric columns. If the precision is nonzero and scale is -127, then it is a FLOAT, else it is a NUMBER(precision, scale). For the case when precision is 0, NUMBER(precision, scale) can be represented simply as NUMBER.

ub1 for explicit describe
sb2 for implicit describe

OCI_ATTR_SCALE

The scale of numeric columns. If the precision is nonzero and scale is -127, then it is a FLOAT, else it is a NUMBER(precision, scale). For the case when precision is 0, NUMBER(precision, scale) can be represented simply as NUMBER.

sb1

OCI_ATTR_IS_NULL

Returns 0 if null values are not permitted for the column. Does not return a correct value for CUBE or ROLLUP operation.

ub1

OCI_ATTR_TYPE_NAME

Returns a string which is the type name. The returned value will contain the type name if the datatype is SQLT_NTY or SQLT_REF. If the datatype is SQLT_NTY, the name of the named datatype's type is returned. If the datatype is SQLT_REF, the type name of the named datatype pointed to by the REF is returned

OraText *

OCI_ATTR_SCHEMA_NAME

Returns a string with the schema name under which the type has been created

OraText *

OCI_ATTR_REF_TDO

The REF of the TDO for the type, if the column type is an object type

OCIRef *

OCI_ATTR_CHARSET_ID

The character set id, if the column is of a string/character type

ub2

OCI_ATTR_CHARSET_FORM

The character set form, if the column is of a string/character type

ub1

Argument and Result Attributes

When a parameter is for an argument of a procedure or function (type OCI_PTYPE_ARG), for a type method argument (type OCI_PTYPE_TYPE_ARG) or for method results (type OCI_PTYPE_TYPE_RESULT), it has the attributes listed in Table 6-14.

Table 6-14 Attributes of Arguments and Results

Attribute Description Attribute Datatype

OCI_ATTR_NAME

Returns a pointer to a string which is the argument name

OraText *

OCI_ATTR_POSITION

The position of the argument in the argument list. Always returns zero.

ub2

OCI_ATTR_TYPECODE

Typecode. See "Datatype Codes".

OCITypeCode

OCI_ATTR_DATA_TYPE

The datatype of the argument. See "Datatype Codes".

ub2

OCI_ATTR_DATA_SIZE

The size of the datatype of the argument. This length is returned in bytes and not characters for strings and raws. It returns 22 for NUMBERs.

ub2

OCI_ATTR_PRECISION

The precision of numeric arguments. If the precision is nonzero and scale is -127, then it is a FLOAT, else it is a NUMBER(precision, scale). For the case when precision is 0, NUMBER(precision, scale) can be represented simply as NUMBER.

b1 for explicit describe

sb2 for implicit describe

OCI_ATTR_SCALE

The scale of numeric arguments. If the precision is nonzero and scale is -127, then it is a FLOAT, else it is a NUMBER(precision, scale). For the case when precision is 0, NUMBER(precision, scale) can be represented simply as NUMBER.

sb1

OCI_ATTR_LEVEL

The datatype levels. This attribute always returns zero.

ub2

OCI_ATTR_HAS_DEFAULT

Indicates whether an argument has a default

ub1

OCI_ATTR_LIST_ARGUMENTS

The list of arguments at the next level (when the argument is of a record or table type).

void *

OCI_ATTR_IOMODE

Indicates the argument mode:

0 is IN (OCI_TYPEPARAM_IN),

1 is OUT (OCI_TYPEPARAM_OUT),

2 is IN/OUT (OCI_TYPEPARAM_INOUT)

OCITypeParamMode

OCI_ATTR_RADIX

Returns a radix (if number type)

ub1

OCI_ATTR_IS_NULL

Returns 0 if null values are not permitted for the column.

ub1

OCI_ATTR_TYPE_NAME

Returns a string which is the type name, or the package name in the case of package local types. The returned value will contain the type name if the datatype is SQLT_NTY or SQLT_REF. If the datatype is SQLT_NTY, the name of the named datatype's type is returned. If the datatype is SQLT_REF, the type name of the named datatype pointed to by the REF is returned.

OraText *

OCI_ATTR_SCHEMA_NAME

For SQLT_NTY or SQLT_REF, returns a string with the schema name under which the type was created, or under which the package was created in the case of package local types

OraText *

OCI_ATTR_SUB_NAME

For SQLT_NTY or SQLT_REF, returns a string with the type name, in the case of package local types

OraText *

OCI_ATTR_LINK

For SQLT_NTY or SQLT_REF, returns a string with the database link name of the database on which the type exists. This can happen only in the case of package local types, when the package is remote.

OraText *

OCI_ATTR_REF_TDO

Returns the REF of the TDO for the type, if the argument type is an object

OCIRef *

OCI_ATTR_CHARSET_ID

Returns the character set ID if the argument is of a string/character type

ub2

OCI_ATTR_CHARSET_FORM

Returns the character set form if the argument is of a string/character type

ub1

List Attributes

When a parameter is for a list of columns, arguments, or subprograms (type OCI_PTYPE_LIST), it has the following type specific attributes and handles (parameters):

The list has an OCI_ATTR_LTYPE attribute which designates the list type. The possible values and their lower bounds when traversing the list are:

Table 6-15 List Attributes

List Attribute Description Lower Bound

OCI_LTYPE_COLUMN

Column list

1

OCI_LTYPE_ARG_PROC

Procedure argument list

1

OCI_LTYPE_ARG_FUNC

Function argument list

0

OCI_LTYPE_SUBPRG

Subprogram list

0

OCI_LTYPE_TYPE_ATTR

Type attribute list

1

OCI_LTYPE_TYPE_METHOD

Type method list

1

OCI_LTYPE_TYPE_ARG_PROC

Type method without result argument list

0

OCI_LTYPE_TYPE_ARG_FUNC

Type method without result argument list

1

OCI_LTYPE_SCH_OBJ

Object list within a schema

0

OCI_LTYPE_DB_SCH

Schema list within a database

0


  • The list has an OCI_ATTR_NUM_PARAMS attribute, which tells the number of elements in the list.

  • Each list has LowerBound .. OCI_ATTR_NUM_PARAMS parameters. LowerBound is the value in the Lower Bound column of Table 6-15, "List Attributes". In the case of a function argument list, position 0 has a parameter for the return value (type OCI_PTYPE_ARG).

Schema Attributes

When a parameter is for a schema type (type OCI_PTYPE_SCHEMA), it has the attributes listed in Table 6-16:

Table 6-16 Attributes Specific to Schemas

Attribute Description Attribute Datatype

OCI_ATTR_LIST_OBJECTS

List of objects in the schema

OCIParam *

Database Attributes

When a parameter is for a database type (type OCI_PTYPE_DATABASE), it has the attributes listed in Table 6-17:

Table 6-17 Attributes Specific to Databases

Attribute Description Attribute Datatype

OCI_ATTR_VERSION

Database version

OraText *

OCI_ATTR_CHARSET_ID

Database character set Id from the server handle

ub2

OCI_ATTR_NCHARSET_ID

Database character set Id from the server handle

ub2

OCI_ATTR_LIST_SCHEMAS

List of schemas (type OCI_PTYPE_SCHEMA) in the database

ub1

OCI_ATTR_MAX_PROC_LEN

Maximum length of a procedure name

ub4

OCI_ATTR_MAX_COLUMN_LEN

Maximum length of a column name

ub4

OCI_ATTR_CURSOR_COMMIT_BEHAVIOR

How a COMMIT operation affects cursors and prepared statements in the database. Values are:

OCI_CURSOR_OPEN - preserve cursor state as before the commit operation

OCI_CURSOR_CLOSED - cursors are closed on COMMIT, but the application can still re-execute the statement without re-preparing it

ub1

OCI_ATTR_MAX_CATALOG_NAMELEN

Maximum length of a catalog (database) name

ub1

OCI_ATTR_CATALOG_LOCATION

Position of the catalog in a qualified table. Values are OCI_CL_START and OCI_CL_END

ub1

OCI_ATTR_SAVEPOINT_SUPPORT

Does database support savepoints? Values are OCI_SP_SUPPORTED and OCI_SP_UNSUPPORTED

ub1

OCI_ATTR_NOWAIT_SUPPORT

Does database support the nowait clause? Values are OCI_NW_SUPPORTED and OCI_NW_UNSUPPORTED

ub1

OCI_ATTR_AUTOCOMMIT_DDL

Is autocommit mode required for DDL statements? Values are OCI_AC_DDL and OCI_NO_AC_DDL

ub1

OCI_ATTR_LOCKING_MODE

Locking mode for the database. Values are OCI_LOCK_IMMEDIATE and OCI_LOCK_DELAYED

ub1

Rule Attributes

When a parameter is for a rule (type OCI_PTYPE_RULE), it has the attributes listed in Table 6-18:

Table 6-18 Attributes Specific to Rules

Attribute Description Attribute Datatype

OCI_ATTR_CONDITION

Rule condition

OraText *

OCI_ATTR_EVAL_CONTEXT_OWNER

Owner name of evaluation context associated with the rule, if any

OraText *

OCI_ATTR_EVAL_CONTEXT_NAME

Object name of evaluation context associated with the rule, if any

OraText *

OCI_ATTR_COMMENT

Comment associated with the rule, if any

OraText *

OCI_ATTR_LIST_ACTION_CONTEXT

List of name value pairs in the action context (type OCI_PTYPE_LIST)

void *

Rule Set Attributes

When a parameter is for a rule set (type OCI_PTYPE_RULE_SET), it has the attributes listed in Table 6-19:

Table 6-19 Attributes Specific to Rule Sets

Attribute Description Attribute Datatype

OCI_ATTR_EVAL_CONTEXT_OWNER

Owner name of evaluation context associated with the rule set, if any

OraText *

OCI_ATTR_EVAL_CONTEXT_NAME

Object name of evaluation context associated with the rule set, if any

OraText *

OCI_ATTR_COMMENT

Comment associated with the rule set, if any

OraText *

OCI_ATTR_LIST_RULES

List of rules in the rule set (type OCI_PTYPE_LIST)

void *

Evaluation Context Attributes

When a parameter is for an evaluation context (type OCI_PTYPE_EVALUATION_CONTEXT), it has the attributes listed in Table 6-20:

Table 6-20 Attributes Specific to Evaluation Contexts

Attribute Description Attribute Datatype

OCI_ATTR_EVALUATION_FUNCTION

Evaluation function associated with the evaluation context, if any

OraText *

OCI_ATTR_COMMENT

Comment associated with the evaluation context, if any

OraText *

OCI_ATTR_LIST_TABLE_ALIASES

List of table aliases in the evaluation context (type OCI_PTYPE_LIST)

void *

OCI_ATTR_LIST_VARIABLE_TYPES

List of variable types in the evaluation context (type OCI_PTYPE_LIST)

void *

Table Alias Attributes

When a parameter is for a table alias (type OCI_PTYPE_TABLE_ALIAS), it has the attributes listed in Table 6-21:

Table 6-21 Attributes Specific to Table Aliases

Attribute Description Attribute Datatype

OCI_ATTR_NAME

Table alias name

OraText *

OCI_ATTR_TABLE_NAME

Table name associated with the alias

OraText *

Variable Type Attributes

When a parameter is for a variable (type OCI_PTYPE_VARIABLE_TYPE), it has the attributes listed in Table 6-22:

Table 6-22 Attributes Specific to Variable Types

Attribute Description Attribute Datatype

OCI_ATTR_NAME

Variable name

OraText *

OCI_ATTR_TYPE

Variable type

OraText *

OCI_ATTR_VAR_VALUE_FUNCTION

Variable value function associated with the variable, if any

OraText *

OCI_ATTR_VAR_METHOD_FUNCTION

Variable method function associated with the variable, if any

OraText *

Name Value Attributes

When a parameter is for a name value pair (type OCI_PTYPE_NAME_VALUE), it has the attributes listed in Table 6-23:

Table 6-23 Attributes Specific to Name Value Pair

Attribute Description Attribute Datatype

OCI_ATTR_NAME

Name

OraText *

OCI_ATTR_VALUE

Value

OCIAnyData*

Character Length Semantics Support in Describing

Since release Oracle9i, query and column information are supported with character length semantics.

The following attributes of describe handles support character length semantics:

  • OCI_ATTR_CHAR_SIZE gets the column character length, which is the number of characters allowed in the column. It is the counterpart of OCI_ATTR_DATA_SIZE that gets the byte length.

  • Calling OCIAttrGet() with attribute OCI_ATTR_CHAR_SIZE or OCI_ATTR_DATA_SIZE does not return data on stored procedure parameters, because stored procedure parameters are not bounded.

  • OCI_ATTR_CHAR_USED gets the type of length semantics of the column. 0 means byte-length semantics and 1 means character length semantics.

An application can describe a select-list query either implicitly or explicitly through OCIStmtExecute(). Other schema elements must be described explicitly through OCIDescribeAny().

Implicit Describing

If the database column was created using character length semantics, then the implicit describe information will contain the character length, the byte length, and a flag indicating how the database column was created. OCI_ATTR_CHAR_SIZE is the character length of the column or expression. The OCI_ATTR_CHAR_USED flag is 1 in this case, indicating that the column or expression was created with character length semantics.

The OCI_ATTR_DATA_SIZE value will be always large enough to hold all the data, as many as OCI_ATTR_CHAR_SIZE number of characters. The OCI_ATTR_DATA_SIZE will be usually set to (OCI_ATTR_CHAR_SIZE)*(the client's max bytes) for each character value.

If the database column was created with byte length semantics, then the implicit describe will behave exactly as it does before release 9.0. That is, the OCI_ATTR_DATA_SIZE value returned will be (column's byte length)*(the maximum conversion ratio between the client and server's character set), that is, column byte length divided by the server's max bytes for each character multiplied by the client's max bytes for each character. The OCI_ATTR_CHAR_USED value is 0 and the OCI_ATTR_CHAR_SIZE value will be set to the same value as OCI_ATTR_DATA_SIZE.

Explicit Describing

Explicit describes of tables will have the following attributes:

  • OCI_ATTR_DATA_SIZE that gets the column's size in bytes, as it appears in the server

  • the length in characters in OCI_ATTR_CHAR_SIZE

  • a flag OCI_ATTR_CHAR_USED that indicates how the column was created

When inserting, if the OCI_ATTR_CHAR_USED flag is set, you can set the OCI_ATTR_MAXCHAR_SIZE in the bind handle to the value returned by OCI_ATTR_CHAR_SIZE in the parameter handle. This will prevent you from violating the size constraint for the column.

See Also:

"IN Binds"

Client and Server Compatibility Issues for Describing

When an Oracle9i or later client talks to an Oracle8i or earlier server, it will behave as if the database is only using byte length semantics;

When an Oracle8i or earlier client talks to a Oracle9i or later server, the attributes OCI_ATTR_CHAR_SIZE and OCI_ATTR_CHAR_USED are not available on the client side.

In both cases, the character length semantics cannot be described when either the server or client has an Oracle8i or earlier software release.

Examples Using OCIDescribeAny()

The following examples demonstrate the use of OCIDescribeAny() for describing different types of schema objects. For a more detailed code sample, see the demonstration program cdemodsa.c included with your Oracle installation.

See Also:

For additional information on the demonstration programs, see Appendix B, "OCI Demonstration Programs"

Retrieving Column Datatypes for a Table

This example illustrates the use of an explicit describe that retrieves the column datatypes for a table.

...
int i=0;
text objptr[] = "EMPLOYEES"; /* the name of a table to be described */
ub2          numcols, col_width;
ub1          char_semantics;
ub2  coltyp;
ub4 objp_len = (ub4) strlen((char *)objptr);
OCIParam *parmh = (OCIParam *) 0;         /* parameter handle */
OCIParam *collsthd = (OCIParam *) 0;      /* handle to list of columns */
OCIParam *colhd = (OCIParam *) 0;         /* column handle */
OCIDescribe *dschp = (OCIDescribe *)0;      /* describe handle */

OCIHandleAlloc((void *)envhp, (void **)&dschp,
        (ub4)OCI_HTYPE_DESCRIBE, (size_t)0, (void **)0);

/* get the describe handle for the table */
if (OCIDescribeAny(svch, errh, (void *)objptr, objp_len, OCI_OTYPE_NAME, 0,
     OCI_PTYPE_TABLE, dschp))
   return OCI_ERROR;

/* get the parameter handle */
if (OCIAttrGet((void *)dschp, OCI_HTYPE_DESCRIBE, (void *)&parmh, (ub4 *)0,
                OCI_ATTR_PARAM, errh))
    return OCI_ERROR;

/* The type information of the object, in this case, OCI_PTYPE_TABLE,
is obtained from the parameter descriptor returned by the OCIAttrGet(). */
/* get the number of columns in the table */
numcols = 0;
if (OCIAttrGet((void *)parmh, OCI_DTYPE_PARAM, (void *)&numcols, (ub4 *)0,
     OCI_ATTR_NUM_COLS, errh))
    return OCI_ERROR;

/* get the handle to the column list of the table */
if (OCIAttrGet((void *)parmh, OCI_DTYPE_PARAM, (void *)&collsthd, (ub4 *)0,
     OCI_ATTR_LIST_COLUMNS, errh)==OCI_NO_DATA)
   return OCI_ERROR;

/* go through the column list and retrieve the data-type of each column,
and then recursively describe column types. */

for (i = 1; i <= numcols; i++)
{
    /* get parameter for column i */
    if (OCIParamGet((void *)collsthd, OCI_DTYPE_PARAM, errh, (void **)&colhd, (ub4)i))
        return OCI_ERROR;

    /* for example, get datatype for ith column */
    coltyp = 0;
    if (OCIAttrGet((void *)colhd, OCI_DTYPE_PARAM, (void *)&coltyp, (ub4 *)0,
       OCI_ATTR_DATA_TYPE, errh))
        return OCI_ERROR;

    /* Retrieve the length semantics for the column */
    char_semantics = 0;
    OCIAttrGet((void*) colhd, (ub4) OCI_DTYPE_PARAM,
                 (void*) &char_semantics,(ub4 *) 0, (ub4) OCI_ATTR_CHAR_USED,
                 (OCIError *) errh);

    col_width = 0;
    if (char_semantics)
        /* Retrieve the column width in characters */
        OCIAttrGet((void*) colhd, (ub4) OCI_DTYPE_PARAM,
                 (void*) &col_width, (ub4 *) 0, (ub4) OCI_ATTR_CHAR_SIZE,
                 (OCIError *) errh);
    else
        /* Retrieve the column width in bytes */
        OCIAttrGet((void*) colhd, (ub4) OCI_DTYPE_PARAM,
                 (void*) &col_width,(ub4 *) 0, (ub4) OCI_ATTR_DATA_SIZE,
                 (OCIError *) errh);
}

if (dschp)
    OCIHandleFree((void *) dschp, OCI_HTYPE_DESCRIBE);
...

Describing the Stored Procedure

The difference between a procedure and a function is that the latter has a return type at position 0 in the argument list, while the former has no argument associated with position 0 in the argument list. The steps required to describe type methods (also divided into functions and procedures) are identical to that of regular PL/SQL functions and procedures. Note that procedures and functions can take default types of objects as arguments. Consider the following procedure:

P1 (arg1 emp.sal%type, arg2 emp%rowtype)

Assume that each row in emp table has two columns: name(VARCHAR2(20)), and sal(NUMBER). In the argument list for P1, there are two arguments, arg1 and arg2, at positions 1 and 2 respectively at level 0, and arguments name and sal at positions 1and 2 respectively at level 1. Description of P1 returns the number of arguments as two while returning the higher level (> 0) arguments as attributes of the 0 zero level arguments.

...
int i = 0, j = 0;
text objptr[] = "add_job_history"; /* the name of a procedure to be described */
ub4 objp_len = (ub4)strlen((char *)objptr);
ub2 numargs = 0, numargs1, pos, level;
text *name, *name1;
ub4 namelen, namelen1;
OCIParam *parmh = (OCIParam *) 0;         /* parameter handle */
OCIParam *arglst = (OCIParam *) 0;          /* list of args */
OCIParam *arg = (OCIParam *) 0;             /* argument handle */
OCIParam *arglst1 = (OCIParam *) 0;          /* list of args */
OCIParam *arg1 = (OCIParam *) 0;             /* argument handle */
OCIDescribe *dschp = (OCIDescribe *)0;      /* describe handle */

OCIHandleAlloc((void *)envhp, (void **)&dschp,
        (ub4)OCI_HTYPE_DESCRIBE, (size_t)0, (void **)0);

/* get the describe handle for the procedure */
if (OCIDescribeAny(svch, errh, (void *)objptr, objp_len, OCI_OTYPE_NAME, 0,
     OCI_PTYPE_PROC, dschp))
   return OCI_ERROR;

/* get the parameter handle */
if (OCIAttrGet((void *)dschp, OCI_HTYPE_DESCRIBE, (void *)&parmh, (ub4 *)0,
         OCI_ATTR_PARAM, errh))
    return OCI_ERROR;

/* Get the number of arguments and the arg list */
if (OCIAttrGet((void *)parmh, OCI_DTYPE_PARAM, (void *)&arglst,
       (ub4 *)0, OCI_ATTR_LIST_ARGUMENTS, errh))
    return OCI_ERROR;

if (OCIAttrGet((void *)arglst, OCI_DTYPE_PARAM, (void *)&numargs, (ub4 *)0,
    OCI_ATTR_NUM_PARAMS, errh))
    return OCI_ERROR;

/* For a procedure, we begin with i = 1; for a
function, we begin with i = 0. */

for (i = 1; i <= numargs; i++) {
  OCIParamGet ((void *)arglst, OCI_DTYPE_PARAM, errh, (void **)&arg, (ub4)i);
  namelen = 0;
  OCIAttrGet((void *)arg, OCI_DTYPE_PARAM, (void *)&name, (ub4 *)&namelen,
       OCI_ATTR_NAME, errh);

  /* to print the attributes of the argument of type record
  (arguments at the next level), traverse the argument list */

  OCIAttrGet((void *)arg, OCI_DTYPE_PARAM, (void *)&arglst1, (ub4 *)0,
        OCI_ATTR_LIST_ARGUMENTS, errh);

  /* check if the current argument is a record. For arg1 in the procedure
  arglst1 is NULL. */

  if (arglst1) {
    numargs1 = 0;
    OCIAttrGet((void *)arglst1, OCI_DTYPE_PARAM, (void *)&numargs1, (ub4 *)0,
         OCI_ATTR_NUM_PARAMS, errh);

    /* Note that for both functions and procedures,the next higher level
    arguments start from index 1. For arg2 in the procedure, the number of
    arguments at the level 1 would be 2 */

    for (j = 1; j <= numargs1; j++) {
      OCIParamGet((void *)arglst1, OCI_DTYPE_PARAM, errh, (void **)&arg1,
          (ub4)j);
      namelen1 = 0;
      OCIAttrGet((void *)arg1, OCI_DTYPE_PARAM, (void *)&name1, (ub4 *)&namelen1,
        OCI_ATTR_NAME, errh);
    }
  }
}

if (dschp)
    OCIHandleFree((void *) dschp, OCI_HTYPE_DESCRIBE);
...

Retrieving Attributes of an Object Type

This example illustrates the use of an explicit describe on a named object type. We illustrate how you can describe an object by its name or by its object reference (OCIRef). The following code fragment attempts to retrieve the datatype value of each of the object type's attributes.

...
int i = 0;
text type_name[] = "inventory_typ";
ub4 type_name_len = (ub4)strlen((char *)type_name);
OCIRef *type_ref = (OCIRef *) 0;
ub2 numattrs = 0, describe_by_name = 1;
ub2 datatype = 0;
OCITypeCode typecode = 0;
OCIDescribe *dschp = (OCIDescribe *) 0;      /* describe handle */
OCIParam *parmh = (OCIParam *) 0;         /* parameter handle */
OCIParam *attrlsthd = (OCIParam *) 0;     /* handle to list of attrs */
OCIParam *attrhd = (OCIParam *) 0;        /* attribute handle */

/* allocate describe handle */
if (OCIHandleAlloc((void *)envh, (void **)&dschp,
                  (ub4)OCI_HTYPE_DESCRIBE, (size_t)0, (void **)0))
   return OCI_ERROR;

/* get the describe handle for the type */
if (describe_by_name) {
  if (OCIDescribeAny(svch, errh, (void *)type_name, type_name_len,
       OCI_OTYPE_NAME, 0, OCI_PTYPE_TYPE, dschp))
       return OCI_ERROR;
}
else {
  /* get ref to type using OCIAttrGet */

  /* get the describe handle for the type */
  if (OCIDescribeAny(svch, errh, (void*)type_ref, 0, OCI_OTYPE_REF,
        0, OCI_PTYPE_TYPE, dschp))
       return OCI_ERROR;
}

/* get the parameter handle */
if (OCIAttrGet((void *)dschp, OCI_HTYPE_DESCRIBE, (void *)&parmh, (ub4 *)0,
        OCI_ATTR_PARAM, errh))
    return OCI_ERROR;

/* The type information of the object, in this case, OCI_PTYPE_TYPE, is
obtained from the parameter descriptor returned by the OCIAttrGet */

/* get the number of attributes in the type */
if (OCIAttrGet((void *)parmh, OCI_DTYPE_PARAM, (void *)&numattrs, (ub4 *)0,
    OCI_ATTR_NUM_TYPE_ATTRS, errh))
    return OCI_ERROR;

/* get the handle to the attribute list of the type */
if (OCIAttrGet((void *)parmh, OCI_DTYPE_PARAM, (void *)&attrlsthd, (ub4 *)0,
      OCI_ATTR_LIST_TYPE_ATTRS, errh))
  return OCI_ERROR;

/* go through the attribute list and retrieve the data-type of each attribute,
and then recursively describe attribute types. */

for (i = 1; i <= numattrs; i++)
{
/* get parameter for attribute i */
if (OCIParamGet((void *)attrlsthd, OCI_DTYPE_PARAM, errh, (void **)&attrhd, i))
      return OCI_ERROR;

/* for example, get datatype and typecode for attribute; note that
OCI_ATTR_DATA_TYPE returns the SQLT code, while OCI_ATTR_TYPECODE returns the
Oracle Type System typecode. */

datatype = 0;
if (OCIAttrGet((void *)attrhd, OCI_DTYPE_PARAM, (void *)&datatype, (ub4 *)0,
               OCI_ATTR_DATA_TYPE,errh))
    return OCI_ERROR;

typecode = 0;
if (OCIAttrGet((void *)attrhd, OCI_DTYPE_PARAM,(void *)&typecode, (ub4 *)0,
               OCI_ATTR_TYPECODE, errh))
    return OCI_ERROR;

/* if attribute is an object type, recursively describe it */
if (typecode == OCI_TYPECODE_OBJECT)
{
  OCIRef *attr_type_ref;
  OCIDescribe *nested_dschp;

  /* allocate describe handle */
  if (OCIHandleAlloc((void *)envh,(void**)&nested_dschp,
    (ub4)OCI_HTYPE_DESCRIBE,(size_t)0, (void **)0))
    return OCI_ERROR;

  if (OCIAttrGet((void *)attrhd, OCI_DTYPE_PARAM,
          (void *)&attr_type_ref, (ub4 *)0, OCI_ATTR_REF_TDO,errh))
    return OCI_ERROR;

   OCIDescribeAny(svch, errh,(void*)attr_type_ref, 0,
          OCI_OTYPE_REF, 0, OCI_PTYPE_TYPE, nested_dschp);
    /* go on describing the attribute type... */
}
}

if (dschp)
    OCIHandleFree((void *) dschp, OCI_HTYPE_DESCRIBE);
...

Retrieving the Collection Element's Datatype of a Named Collection Type

This example illustrates the use of an explicit describe on a named collection type:

text type_name[] = "phone_list_typ";
ub4 type_name_len = (ub4) strlen((char *)type_name);
OCIRef *type_ref = (OCIRef *) 0;
ub2 describe_by_name = 1;
ub4 num_elements = 0;
OCITypeCode typecode = 0, collection_typecode = 0, element_typecode = 0;
void *collection_element_parmh = (void *) 0;
OCIDescribe *dschp = (OCIDescribe *) 0;      /* describe handle */
OCIParam *parmh = (OCIParam *) 0;         /* parameter handle */

/* allocate describe handle */
if (OCIHandleAlloc((void *)envh, (void **)&dschp,
                  (ub4)OCI_HTYPE_DESCRIBE, (size_t)0, (void **)0))
   return OCI_ERROR;

/* get the describe handle for the type */
if (describe_by_name) {
  if (OCIDescribeAny(svch, errh, (void *)type_name, type_name_len,
       OCI_OTYPE_NAME, 0, OCI_PTYPE_TYPE, dschp))
       return OCI_ERROR;
}
else {
  /* get ref to type using OCIAttrGet */

  /* get the describe handle for the type */
  if (OCIDescribeAny(svch, errh, (void*)type_ref, 0, OCI_OTYPE_REF,
        0, OCI_PTYPE_TYPE, dschp))
       return OCI_ERROR;
}

/* get the parameter handle */
if (OCIAttrGet((void *)dschp, OCI_HTYPE_DESCRIBE, (void *)&parmh, (ub4 *)0,
        OCI_ATTR_PARAM, errh))
    return OCI_ERROR;

/* get the Oracle Type System type code of the type to determine that this is a
collection type */
typecode = 0;
if (OCIAttrGet((void *)parmh, OCI_DTYPE_PARAM,(void *)&typecode, (ub4 *)0,
      OCI_ATTR_TYPECODE, errh))
    return OCI_ERROR;

/* if typecode is OCI_TYPECODE_NAMEDCOLLECTION,
  proceed to describe collection element */
if (typecode == OCI_TYPECODE_NAMEDCOLLECTION)
{
  /* get the collection's type: ie, OCI_TYPECODE_VARRAY or OCI_TYPECODE_TABLE */
  collection_typecode = 0;
  if (OCIAttrGet((void *)parmh, OCI_DTYPE_PARAM, (void *)&collection_typecode,
 (ub4 *)0,
       OCI_ATTR_COLLECTION_TYPECODE, errh))
    return OCI_ERROR;

  /* get the collection element; you MUST use this to further retrieve information
     about the collection's element */
  if (OCIAttrGet((void *)parmh, OCI_DTYPE_PARAM, &collection_element_parmh,
                 (ub4 *)0,
        OCI_ATTR_COLLECTION_ELEMENT, errh))
    return OCI_ERROR;
  /* get the number of elements if collection is a VARRAY; not valid for nested
     tables */
  if (collection_typecode == OCI_TYPECODE_VARRAY) {
    if (OCIAttrGet((void *)collection_element_parmh, OCI_DTYPE_PARAM,
          (void *)&num_elements, (ub4 *)0, OCI_ATTR_NUM_ELEMS, errh))
      return OCI_ERROR;
  }
  /* now use the collection_element parameter handle to retrieve information about
     the collection element */
  element_typecode = 0;
  if (OCIAttrGet((void *)collection_element_parmh, OCI_DTYPE_PARAM,
        (void *)&element_typecode, (ub4 *)0, OCI_ATTR_TYPECODE, errh))
    return OCI_ERROR;

  /* do the same to describe additional collection element information; this is
  very similar to describing type attributes */
}

if (dschp)
    OCIHandleFree((void *) dschp, OCI_HTYPE_DESCRIBE);
...

Describing with Character Length Semantics

The following sample code shows a loop that retrieves the column names and datatypes corresponding to a query following query execution. The query was associated with the statement handle by a prior call to OCIStmtPrepare().

...
OCIParam     *mypard = (OCIParam *) 0;
ub2          dtype;
text         *col_name;
ub4          counter, col_name_len, char_semantics;
ub2          col_width;
sb4          parm_status;

text *sqlstmt = (text *)"SELECT * FROM employees WHERE employee_id = 100";

checkerr(errhp, OCIStmtPrepare(stmthp, errhp, (OraText *)sqlstmt,
                    (ub4)strlen((char *)sqlstmt),
                    (ub4) OCI_NTV_SYNTAX, (ub4) OCI_DEFAULT));
checkerr(errhp, OCIStmtExecute(svchp, stmthp, errhp, 0, 0, (OCISnapshot *)0, (OCISnapshot *)0, OCI_DEFAULT));

/* Request a parameter descriptor for position 1 in the select-list */
counter = 1;
parm_status = OCIParamGet((void *)stmthp, OCI_HTYPE_STMT, errhp,
               (void **)&mypard, (ub4) counter);
/* Loop only if a descriptor was successfully retrieved for
   current position, starting at 1 */
while (parm_status == OCI_SUCCESS) {
   /* Retrieve the datatype attribute */
   checkerr(errhp, OCIAttrGet((void*) mypard, (ub4) OCI_DTYPE_PARAM,
           (void*) &dtype,(ub4 *) 0, (ub4) OCI_ATTR_DATA_TYPE,
           (OCIError *) errhp  ));
   /* Retrieve the column name attribute */
   col_name_len = 0;
   checkerr(errhp, OCIAttrGet((void*) mypard, (ub4) OCI_DTYPE_PARAM,
           (void**) &col_name, (ub4 *) &col_name_len, (ub4) OCI_ATTR_NAME,
           (OCIError *) errhp ));
   /* Retrieve the length semantics for the column */
   char_semantics = 0;
   checkerr(errhp, OCIAttrGet((void*) mypard, (ub4) OCI_DTYPE_PARAM,
           (void*) &char_semantics,(ub4 *) 0, (ub4) OCI_ATTR_CHAR_USED,
           (OCIError *) errhp  ));
   col_width = 0;
   if (char_semantics)
       /* Retrieve the column width in characters */
       checkerr(errhp, OCIAttrGet((void*) mypard, (ub4) OCI_DTYPE_PARAM,
               (void*) &col_width, (ub4 *) 0, (ub4) OCI_ATTR_CHAR_SIZE,
               (OCIError *) errhp  ));
   else
       /* Retrieve the column width in bytes */
       checkerr(errhp, OCIAttrGet((void*) mypard, (ub4) OCI_DTYPE_PARAM,
               (void*) &col_width,(ub4 *) 0, (ub4) OCI_ATTR_DATA_SIZE,
               (OCIError *) errhp  ));
   /* increment counter and get next descriptor, if there is one */
   counter++;
   parm_status = OCIParamGet((void *)stmthp, OCI_HTYPE_STMT, errhp,
          (void **)&mypard, (ub4) counter);
} /* while */
...