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 Rdb/VMS
 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.

Additional information available:

FormatExample

 ON ERROR ─┬─> statement ─┬─> 
E
N
D
E
R
R
O
R
           └────────<─────┘

 statement

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

 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$MATCH_COND.  This run-time library procedure
     matches the condition value that Rdb/VMS returns to the program
     (RDB$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.