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:

FormatExampleMore

 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.

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