HP 3000 Manuals HP 3000 Manuals
Defining Transactions You define transactions in the PROCEDURE DIVISION to control what changes are committed to a DBEnvironment and when they are committed. A transaction consists of all the SQL commands that are executed between a BEGIN WORK command and either a COMMIT WORK command or a ROLLBACK WORK command. When a COMMIT WORK command is successfully executed, all operations performed within the transaction are permanent in the DBEnvironment. When a ROLLBACK WORK command is executed, none of the changes remain in the DBEnvironment. The number and duration of transactions in an application program depends on such factors a concurrency and data consistency. For detailed information regarding transaction management, see the ALLBASE/SQL Reference Manual . The commands at 4 and 5 in Figure 3-1 start and end a transaction that consists of a single execution of the SELECT command in paragraph B100-SELECT-DATA. The BEGIN WORK command in paragraph A300-BEGIN-TRANSACTION is optional, but recommended. If you omit a BEGIN WORK command, ALLBASE/SQL automatically issues a BEGIN WORK on your behalf before executing the first SQL command that requires that a transaction be in progress. The COMMIT WORK command in paragraph A400-END-TRANSACTION terminates the transaction after each execution of the SELECT command. Because the program does no DBEnvironment updates, this command is used to terminate the transaction even if an error is encountered. In programs that update data in a DBEnvironment, a ROLLBACK WORK command could be used to undo the effects of any database changes that occurred during a transaction before the error occurred.