1  ON_ERROR
   Specifies the statement(s) the host language will perform if
   an error occurs during the execution of the associated data
   manipulation statement. The statements can be host language
   statements or Oracle Rdb data manipulation statements.

                                  NOTE

      ON ERROR is supported only for the high-level language
      preprocessors. ON ERROR is not supported for RDO or Callable
      RDO.
 

2  Format

 (B)0ON ERROR qwq> statement qwq> END_ERROR
           mqqqqqqqq<qqqqqj

   statement

   Any valid host language statement or Oracle Rdb data manipulation
   statement. Separate multiple statements with the appropriate
   delimiter or terminator according to the rules of the host
   language.
 

2  Example
   This BASIC program uses LIB$MATCH_COND to handle errors that
   occur in the MODIFY statement:

   30
   &RDB& START_TRANSACTION READ_WRITE

   45  !  Input data
       !
       PRINT
       INPUT "enter status code"; STATUS_CODE
       PRINT
       INPUT "enter status name"; STATUS_NAME
       PRINT
       INPUT "enter status type"; STATUS_TYPE

   50 !  Modify the record
      !
   &RDB& FOR W IN WORK_STATUS
   &RDB&      MODIFY W USING
   &RDB&        ON ERROR
                  GOSUB 1000
   &RDB&        END_ERROR
   &RDB&        W.STATUS_CODE = STATUS_CODE;
   &RDB&        W.STATUS_NAME = STATUS_NAME;
   &RDB&        W.STATUS_TYPE = STATUS_TYPE
   &RDB&      END_MODIFY
            PRINT
            PRINT STATUS_CODE, STATUS_NAME, STATUS_TYPE
   &RDB& END_FOR
         GO TO 5000

   1000 MATCH_COND =             &
        LIB$MATCH_COND(RDB$STATUS,RDB$_NOT_VALID)

        SELECT MATCH_COND

        CASE 1
           PRINT "You have entered invalid data.  Try again."
           CALL SYS$PUTMSG(RDB$MESSAGE_VECTOR)
   &RDB&     ROLLBACK
           GOTO 20

        CASE 0
           PRINT "Unknown error"
           CALL SYS$PUTMSG(RDB$MESSAGE_VECTOR)
   &RDB&     ROLLBACK
           GO TO 5000

        END SELECT

        RETURN

   5000
   &RDB&   FINISH
           END

   This excerpt from a BASIC program performs the following actions:

   o  Prompts for input for the MODIFY statement.

   o  Starts a FOR loop.

   o  If an error occurs in the MODIFY statement, the program
      branches to the call to LIB$MATCH_COND. This run-time library
      procedure matches the condition value that Oracle Rdb returns
      to the program (RDB$STATUS) with the condition code RDB$_NOT_
      VALID. If the return status is RDB$_NOT_VALID, the program
      prints the appropriate message and loops back to prompt again.
      If some other error code is detected, "Unknown error" is
      displayed and the program stops.
 

2  More
   If you have invoked a database, you have the necessary privileges
   to use the ON_ERROR clause.