SQL Reference

Effect of DESCRIBE on the SQLDA

For a DESCRIBE or PREPARE INTO statement, the database manager always sets SQLD to the number of columns in the result set.

The SQLVARs in the SQLDA are set in the following cases:

SQLN >= SQLD and no column is either a LOB, user-defined type or reference type
The first SQLD SQLVAR entries are set and SQLDOUBLED is set to blank.
SQLN >= 2*SQLD and at least one column is a LOB, user-defined type or reference type
Two times SQLD SQLVAR entries are set and SQLDOUBLED is set to '2'.
SQLD <= SQLN < 2*SQLD and at least one column is a distinct type or reference type but there are no LOB columns or structured type columns
The first SQLD SQLVAR entries are set and SQLDOUBLED is set to blank. If the SQLWARN bind option is YES, a warning SQLCODE +237 (SQLSTATE 01594) is issued.

The SQLVARs in the SQLDA are NOT set (requiring allocation of additional space and another DESCRIBE) in the following cases:

SQLN < SQLD and no column is either a LOB, user-defined type or reference type
No SQLVAR entries are set and SQLDOUBLED is set to blank. If the SQLWARN bind option is YES, a warning SQLCODE +236 (SQLSTATE 01005) is issued.
Allocate SQLD SQLVARs for a successful DESCRIBE.
SQLN < SQLD and at least one column is a distinct type or reference type but there are no LOB columns or structured type columns
No SQLVAR entries are set and SQLDOUBLED is set to blank. If the SQLWARN bind option is YES, a warning SQLCODE +239 (SQLSTATE 01005) is issued.
Allocate 2*SQLD SQLVARs for a successful DESCRIBE including the names of the distinct types and target types of reference types.
SQLN < 2*SQLD and at least one column is a LOB or a structured type
No SQLVAR entries are set and SQLDOUBLED is set to blank. A warning SQLCODE +238 (SQLSTATE 01005) is issued (regardless of the setting of the SQLWARN bind option).
Allocate 2*SQLD SQLVARs for a successful DESCRIBE.

References in the above lists to LOB columns include distinct type columns whose source type is a LOB type.

The SQLWARN option of the BIND or PREP command is used to control whether the DESCRIBE (or PREPARE INTO) will return the warning SQLCODEs +236, +237, +239. It is recommended that your application code always consider that these SQLCODEs could be returned. The warning SQLCODE +238 is always returned when there are LOB or structured type columns in the select list and there are insufficient SQLVARs in the SQLDA. This is the only way the application can know that the number of SQLVARs must be doubled because of a LOB or structured type column in the result set.

If a structured type column is being described, but no FROM SQL transform is defined (either because no TRANSFORM GROUP was specified using the CURRENT DEFAULT TRANSFORM GROUP special register (SQLSTATE 42741), or because the name group does not have a FROM SQL transform function defined (SQLSTATE 42744), the DESCRIBE will return an error. This error is the same error returned for a DESCRIBE of a table with a structured type column.

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