SQL Server returns information about a results set before it returns the data in the results set. The SQL Server driver returns this information to an application through the SQLColAttributes, SQLDescribeCol, and SQLNumResultCols functions.
When connected to SQL Server 6.x, the SQL Server driver uses the SET FMTONLY statement to retrieve the appropriate information about a results set.
When connected to SQL Server 4.2x, if an application calls any of these functions after a SELECT statement has been prepared and before it has been executed, the SQL Server driver submits the SELECT statement with the clause WHERE 1=2. This forces SQL Server to generate a results set without any rows but with the information about the results set.
Note When connected to SQL Server 4.2x, SQLColAttributes, SQLDescribeCol, and SQLNumResultCols cannot return information about a results set that is generated by a procedure if that procedure has been prepared but not executed. If the SELECT statement is the first statement in a batched statement and SQL Server native grammar is used (no semicolons between statements), the results of these functions are unpredictable. Note also that the word "SELECT" must be the first token in the buffer. If anything precedes the word "SELECT" in the statement to be prepared, "WHERE 1=2" will not be added to the SELECT statement and the information about the results set will not be returned.
In SQL Server 6.5, the ODBC SQL Server driver supports the following driver-specific column attributes in SQLColAttributes.
| fDescType parameter | pfDesc values |
|---|---|
| SQL_CA_SS_COLUMN_SSTYPE | SQLTEXT SQLVARBINARY SQLINTN SQLVARCHAR SQLBINARY SQLIMAGE SQLCHAR SQLINT1 SQLBIT SQLINT2 SQLINT4 SQLMONEY SQLDATETIME SQLFLT8 SQLFLTN SQLMONEYN SQLDATETIMN SQLFLT4 SQLMONEY4 SQLDATETIM4 SQLDECIMAL SQLDECIMALN SQLNUMERIC SQLNUMERICN (Similar to dbcoltype or dbalttype.) |
| SQL_CA_SS_COLUMN_UTYPE | SQLudtTEXT SQLudtVARBINARY SQLudtINTN SQLudtVARCHAR SQLudtBINARY SQLudtIMAGE SQLudtCHAR SQLudtINT1 SQLudtBIT SQLudtINT2 SQLudtINT4 SQLudtMONEY SQLudtDATETIME SQLudtFLT8 SQLudtFLTN SQLudtMONEYN SQLudtDATETIMN SQLudtSYSNAME SQLudtTIMESTAMP SQLudtFLT4 SQLudtMONEY4 SQLudtDATETIM4 SQLudtDECML SQLudtDECMLN SQLudtNUM SQLudtNUMN (Similar to dbcolutype or dbaltutype.) |
| SQL_CA_SS_NUM_ORDERS | The number of columns in the SQL statement's ORDER BY clause. (Similar to dbnumorders.) |
| SQL_CA_SS_COLUMN_ORDER | The SELECT list column ID of a column that appears in the SQL statement's ORDER BY clause. (Similar to dbordercol.) |
| SQL_CA_SS_COLUMN_VARYLEN | TRUE if the column's data can vary in length, otherwise FALSE. (Similar to dbvarylen.) |
| SQL_CA_SS_NUM_COMPUTES | The number of compute clauses in the current results set. (Similar to dbnumcompute.) |
| SQL_CA_SS_COMPUTE_ID | The compute ID of a compute row. (Similar to dbnextrow compute ID return value.) |
| SQL_CA_SS_COMPUTE_BYLIST | The bylist for a compute row. (Similar to dbbylist.) |
| SQL_CA_SS_COLUMN_ID | The SELECT list column ID for a compute column. (Similar to dbaltcolid.) |
| SQL_CA_SS_COLUMN_OP | SQLAOPCNT SQLAOPSUM SQLAOPAVG SQLAOPMIN SQLAOPMAX SQLAOPANY SQLAOPNOOP (Similar to dbaltop.) |