I have come across two versions of an SQLRPGLE program and saw a change in the code as below:
Before:
Exec Sql SELECT 'N'
INTO :APRFLG
FROM LG751F T1
INNER JOIN LG752F T2
ON T1.ISBOLN = T2.IDBOLN AND
T1.ISITNO = T2.IDMDNO
WHERE T2.IDVIN = :M_VIN AND
T1.ISAPRV <> 'Y';
After:
Exec Sql SELECT case
when T1.ISAPRV <> 'Y' then 'N'
else T1.ISAPRV
end as APRFLG
INTO :APRFLG
FROM LG751F T1
join LG752F T2
ON T1.ISBOLN = T2.IDBOLN AND
T1.ISITNO = T2.IDMDNO
WHERE T2.IDVIN = :M_VIN AND
T1.ISAPRV <> 'Y'
group by T1.ISAPRV;
Could you please tell me if you see any difference in how the codes would work differently? The second SQL has a group by which is supposed to be a fix to avoid -811 SQLCod error. Apart from this, do you guys spot any difference?
They are both examples of poor coding IMO.
The requirement to "remove duplicates" is often an indication of a bad statement design and/or a bad DB design.
You appear to be doing an existence check, in which case you should be making use of the EXISTS predicate.
select 'N' into :APRFLG
from sysibm.sysdummy1
where exists (select 1
FROM LG751F T1
INNER JOIN LG752F T2
ON T1.ISBOLN = T2.IDBOLN
AND T1.ISITNO = T2.IDMDNO
WHERE
T2.IDVIN = :M_VIN
AND T1.ISAPRV <> 'Y');
As far as the original two statements, besides the group by, the only real difference is moving columns from the JOIN clause to the WHERE clause. However, the query engine in Db2 for i will rewrite both statements equivalently and come up with the same plan; since an inner join is used.
EDIT : as Mark points out, there JOIN and WHERE are the same in both the OP's statements. But I'll leave the statement above in as an FYI.