Purging records on AS/400

Question

I have to delete some records that are considered to be useless.

There is a address file and an order history file. In the company which has a consumer products, they get many product inquiries or start of sale that never becomes a sale.

Each inquiry gets a record in the address file, Customer number. In the order history file is same customer numn and a Suffix field. which is started at 000 and increments when there is new order. the bulk of the business is in fact a recurring model.

A customer who has only '000' record (there could be multiple 000's), means they never bought anything we wish to purge them from these files.

I am thinking a simple RPG program but am also interested in just using SQL if that is possible or other methods.

At this stage, we would not actually be deleting but copying the proposed records for purging to an output file which will be reviewed and also would be stored in case a need to revert.

F Addressfile   IF  E

F OrderHistory  IF  E

**** create 2 output file clones but with altered name for now.

F Zaddressfile  O  E
F ZorderHistory O  E


                  *inlr    doweq *off
                           Read  Addressfile          lr
                  *inlr    ifeq *off
                           move  *off      Flg000
                           exsr  Chk000
                   Flg000  ifeq  *on
                           iter
                           else  exsr      purge
                           endif
                           endif
                           enddo

                   Chk000  begsr

**basically setll to a different logical on the orderhistory and reade for a long as we have the matching customer number and if there is a suffix not = 000 then we turn on the flag and get out.

the purge subr will have to read thru again to get the records needed to purge from the orderhistory file by using the same customer number that would still be in the read of the address file. because i would not be sure what value has the subr, for customer and i dont want to store that.

then it would write to the new file incl the address file then we can iter read the next customer in address file.

also we cannot assume that if someone did buy, they have a 001 maybe it got deleted over the years.

if we did, i could simply chain on that.

Answer 1

All sorts of steps you have to do in RPG. This can be done in SQL a variety of simpler ways. SQL is adept at processing and analyzing groups of records in an entire file all at once.

CREATE TABLE zaddresses AS
( SELECT *
    FROM addressFile
    WHERE cust IN (SELECT cust 
                     FROM orderHistory
                     GROUP BY cust
                     HAVING max(sufix)='000'
                  )
) 
WITH DATA
NOT LOGGED INITIALLY;

CREATE TABLE zorderHst AS 
( SELECT * 
    FROM orderHistory
    WHERE cust IN (SELECT cust 
                     FROM zaddresses
                  )
)
WITH DATA
NOT LOGGED INITIALLY;

There, you've defined your holding table and populated it in one single statement each. It does have some nested logic, but nonetheless only two statements.

To purge them

DELETE FROM addressfile
  WHERE cust IN (SELECT cust FROM zaddresses);

DELETE FROM orderHistory
  WHERE cust IN (SELECT cust FROM zaddresses);

A grand total of four SQL statements. (I wont even ask how many you'd have in your RPG program)

Once you understand SQL, you can think about processing entire files, not just record by record instructions. It's much simpler to get things done, and it's almost always faster when done well.

(You may hear arguments about performance under particular circumstances, but most often they simply aren't using SQL as well as they should. If you write poor RPG, it performs badly too. ;-)

Answer 2

I would use SQL.

-- Save only the rows to be deleted
CREATE TABLE ZADDRESSFILE AS
   (SELECT *
    FROM   ADDRESSFILE af
    WHERE  NOT EXISTS
        (SELECT 1
         FROM ADDRESSFILE sub
         WHERE sub.CUSTNO = af.CUSTNO
         AND   sub.SUFFIX <> '000' -- (or <> 0 if numeric)
         )
    )

-- If ZADDRESSFILE exists and you want to add the rows 
-- to ZADDRESSFILE instead....
INSERT INTO ZADDRESSFILE
   (SELECT *
    FROM   ADDRESSFILE af
    WHERE  NOT EXISTS
        (SELECT 1
         FROM ADDRESSFILE sub
         WHERE sub.CUSTNO = af.CUSTNO
         AND   sub.SUFFIX <> '000' -- (or <> 0 if numeric)
         )
    AND OT EXISTS
         (SELECT 1
          FROM ZADDRESSFILE sub
          WHERE sub.CUSTNO = af.CUSTNO
          )
    )


-- Get number of rows to be deleted
SELECT COUNT(*)
FROM ADDRESSFILE af
WHERE NOT EXISTS
   (SELECT 1
    FROM   ADDRESSFILE sub
    WHERE  sub.CUSTNO = af.CUSTNO
    AND    sub.SUFIX <> '000'
    )


-- Delete 'em
DELETE
FROM ADDRESSFILE af
WHERE NOT EXISTS
   (SELECT 1
    FROM   ADDRESSFILE sub
    WHERE  sub.CUSTNO = af.CUSTNO
    AND    sub.SUFIX <> '000'
    )