describe output (SQL descriptor)

Obtains row format information about the result set of a prepared dynamic SQL statement.

exec sql describe [output] statement_name 
 using sql descriptor descriptor_name end-exec

output: An optional keyword that has no effect on the describe output statement but provides conformance to the SQL standard.

statement_name: The name (specified in a prepare statement) that represents the select statement to be executed.

descriptor_name: The name of a SQL descriptor that is to store the information returned by the describe output statement.

EXEC SQL BEGIN DECLARE SECTION END-EXEC.

          01      QUERY        PIC X(100).

          01      NOUT         PIC S9(9) COMP.

          01      DATAVAL      PIC X(100).

          01      COUNTER      PIC S9(9) COMP.

          01      NUMCOLS      PIC S9(9) COMP.

          01      COLNAME      PIC X(32).

          01      COLTYPE      PIC S9(9) COMP.

          01      COLLEN       PIC S9(9) COMP.

 EXEC SQL END DECLARE SECTION END-EXEC.

...

 DISPLAY "ENTER QUERY :"

 ACCEPT QUERY.

 EXEC SQL ALLOCATE DESCRIPTOR desc_out WITH MAX 256 END-EXEC.

 EXEC SQL PREPARE dynstmt FROM :QUERY END-EXEC.

 EXEC SQL DECLARE selcursor CURSOR FOR dynstmt END-EXEC.

 EXEC SQL OPEN selcursor USING SQL DESCRIPTOR desc_out END-EXEC.

 EXEC SQL DESCRIBE OUTPUT dynstmt USING SQL DESCRIPTOR desc_out END-EXEC.

 PERFORM  FETCH-LOOP UNTIL SQLCODE = 100.

 EXEC SQL CLOSE selcursor END-EXEC.

 EXEC SQL DEALLOCATE CURSOR selcursor END-EXEC.

 EXEC SQL DEALLOCATE PREPARE dynstmt END-EXEC.

 EXEC SQL DEALLOCATE DESCRIPTOR desc_out END-EXEC.

...

 FETCH-LOOP.

      EXEC SQL FETCH selcursor INTO SQL DESCRIPTOR desc_out END-EXEC

      EXEC SQL GET DESCRIPTOR desc_out :NOUT = COUNT END-EXEC

      DISPLAY "COLS RETRIEVED = ", NOUT

      MOVE 1 TO COUNTER

      PERFORM GET-DESC-PARA UNTIL  COUNTER > NOUT.

  END-FETCH-LOOP.

  GET-DESC-PARA.

       EXEC SQL GET DESCRIPTOR desc_out VALUE :COUNTER

                        :COLNAME = NAME,

                        :COLTYPE = TYPE,

                        :COLLEN  = LENGTH

                     END-EXEC

         DISPLAY "NAME      :", COLNAME

         DISPLAY "TYPE      :", COLTYPE

         DISPLAY "LENGTH    :", COLLEN

         EXEC SQL GET DESCRIPTOR desc_out VALUE :COUNTER

                          :DATAVAL = DATA END-EXEC

         DISPLAY "DATA      :", DATAVAL

         DISPLAY " "

         ADD 1 TO COUNTER.

   END-GET-DESC-PARA.

The information obtained is the type, name, length (or precision and scale, if a number), nullable status, and number of items in the result set.
The information is about the result columns from the select column list.
Execute this statement before the prepared statement executes. If you perform a describe output statement after you execute and before you perform a get descriptor, the results will be discarded.