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:
The first SQLD SQLVAR entries are set and SQLDOUBLED is set to blank.
Two times SQLD SQLVAR entries are set and SQLDOUBLED is set to '2'.
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:
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.
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.
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 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 column in the result set.