PostgreSQL
Synopsis
GET DESCRIPTOR descriptor_name :cvariable = descriptor_header_item [, ... ]
GET DESCRIPTOR descriptor_name VALUE column_number :cvariable = descriptor_item [, ... ]Description
GET DESCRIPTOR retrieves information about a query result set from an SQL descriptor area and stores it into host variables. A descriptor area is typically populated using FETCH or SELECT before using this command to transfer the information into host language variables.
This command has two forms: The first form retrieves descriptor “[.quote]#header”# items, which apply to the result set in its entirety. One example is the row count. The second form, which requires the column number as additional parameter, retrieves information about a particular column. Examples are the column name and the actual column value.
Parameters
- `descriptor_name`
-
A descriptor name.
- `descriptor_header_item`
-
A token identifying which header information item to retrieve. Only
COUNT, to get the number of columns in the result set, is currently supported. - `column_number`
-
The number of the column about which information is to be retrieved. The count starts at 1.
- `descriptor_item`
-
A token identifying which item of information about a column to retrieve. See Section 36.7.1 for a list of supported items.
- `cvariable`
-
A host variable that will receive the data retrieved from the descriptor area.
Examples
An example to retrieve the number of columns in a result set:
EXEC SQL GET DESCRIPTOR d :d_count = COUNT;An example to retrieve a data length in the first column:
EXEC SQL GET DESCRIPTOR d VALUE 1 :d_returned_octet_length = RETURNED_OCTET_LENGTH;An example to retrieve the data body of the second column as a string:
EXEC SQL GET DESCRIPTOR d VALUE 2 :d_data = DATA;Here is an example for a whole procedure of executing SELECT current_database(); and showing the number of columns, the column data length, and the column data:
int
main(void)
{
EXEC SQL BEGIN DECLARE SECTION;
int d_count;
char d_data[1024];
int d_returned_octet_length;
EXEC SQL END DECLARE SECTION;
EXEC SQL CONNECT TO testdb AS con1 USER testuser;
EXEC SQL SELECT pg_catalog.set_config('search_path', '', false); EXEC SQL COMMIT;
EXEC SQL ALLOCATE DESCRIPTOR d;
/* Declare, open a cursor, and assign a descriptor to the cursor */
EXEC SQL DECLARE cur CURSOR FOR SELECT current_database();
EXEC SQL OPEN cur;
EXEC SQL FETCH NEXT FROM cur INTO SQL DESCRIPTOR d;
/* Get a number of total columns */
EXEC SQL GET DESCRIPTOR d :d_count = COUNT;
printf("d_count = %d\n", d_count);
/* Get length of a returned column */
EXEC SQL GET DESCRIPTOR d VALUE 1 :d_returned_octet_length = RETURNED_OCTET_LENGTH;
printf("d_returned_octet_length = %d\n", d_returned_octet_length);
/* Fetch the returned column as a string */
EXEC SQL GET DESCRIPTOR d VALUE 1 :d_data = DATA;
printf("d_data = %s\n", d_data);
/* Closing */
EXEC SQL CLOSE cur;
EXEC SQL COMMIT;
EXEC SQL DEALLOCATE DESCRIPTOR d;
EXEC SQL DISCONNECT ALL;
return 0;
}When the example is executed, the result will look like this:
d_count = 1
d_returned_octet_length = 6
d_data = testdb