DB2/Cursor program working in cobol

问题

My requirement is to delete data from db2 table which contains duplicate phone num(invalid phone num, set of 16 phone numbers which is hardcoded).And one phone num should be retained , that depends on sequence number(minimum value).

consider main table has following data : PHONE_TAB

Client_Id   Phone_num  Seq_num
 1234        45678       15   --- delete
 4444        55555       45
 1234        45678       10   ---should be retained 
 5555        22222       25
 1234        45678       20   ---  delete
 1234        45678       11   ---  delete

Note : also i have to move the rows which will be deleted to output tape file before deleting to take backup.

Have come up with the below logic, Declaring cursor :

EXEC SQL
  DECLARE CUR1 CURSOR WITH HOLD FOR
   SELECT * FROM PHONE_TAB WHERE PHONE_NUM = 45678
END-EXEC

FETCH-PARA

EXEC SQL
 FETCH CUR1 INTO :DCLGEN_CLIENT_ID
                :DCLGEN_PHONE_NUM
                :DCLGEN_SEQ_NUM
END-EXEC

VALIDATE-PARA

EXEC SQL
 SELECT MIN(SEQ_NUM) FROM PHONE_TAB
 WHERE CLIENT_ID = :DCLGEN_CLIENT_ID
       PHONE_NUM = :DCLGEN_PHONE_NUM GROUP BY CLIENT_ID AND PHONE_NUM
       INTO WS_MIN
END-EXEC

EVALUATE TRUE 
 WHEN SEQ_NUM > WS_MIN 
      PERFORM BACKUP-PARA
 WHEN OTHER
      PERFORM FETCH-PARA

Finally , DELETE-PARA

EXEC SQL
  DELETE FROM PHONE_TAB WHERE CURRENT CURSOR
END-EXEC

Can someone tell me whether this logic is right ? My doubt is whether it will do mass deletion without taking backup to tape file?

Thanks

回答1:

You can delete them all in one go with the following SQL

DELETE FROM PHONE_TAB A
 WHERE EXISTS (SELECT 1 FROM PHONE_TAB B
                WHERE A.PHONE_NUM = B.PHONE_NUM AND
                      A.SEQ_NUM > B.SEQ_NUM)

It works by deleting all rows where another row exists that has the same phone number and a lower sequence number.

You can check that it deletes the right rows by first running it with a select, like this

SELECT * FROM PHONE_TAB A
 WHERE EXISTS (SELECT 1 FROM PHONE_TAB B
                WHERE A.PHONE_NUM = B.PHONE_NUM AND
                      A.SEQ_NUM > B.SEQ_NUM)

If you need to backup the rows, you can run the select and then delete the rows.

来源：https://stackoverflow.com/questions/47251141/db2-cursor-program-working-in-cobol

标签

sql

db2

cursor

cobol

mainframe