Re: next baby step in SQL: start using join

[Vern Hamberg <vhamberg@xxxxxxxxxxxxxxxxxxxxxxxxx>]

This is how Query/400 does joins - with the WHERE clause. And how we all 
did this before AS/400 gave us the JOIN clause. The first 4 tests in the 
WHERE clause are your JOIN specs - go back to your Query/400 definition in 
the file specification and compare to those.

RTVQMQRY does not handle type 2 or 3 joins from Query/400 - makes then all 
type 1 - so be sure to check if you have those in the query definition.

Basically, the first 4 tests are put into the ON clause of the JOIN, the 
last 2 stay in the WHERE clause.

If you have type 2 or 3, you need to use a LEFT OUTER join or an EXCEPTION 
join.

HTH

Vern

At 01:04 PM 3/27/2003 -0800, you wrote:
> I'm somewhat of an experienced simple user of SQL, i.e., never done any joins.
>
> I am now have what appears to be a perfect opportunity to use SQL join to 
> greatly simplify my
> coding.  Knowing that one can use Retrieve Query Mgmt Query (RTVQMQRY) to 
> take a *QRYDFN and
> generate the SQL via ALWQRYDFN(*YES), I use WRKQRY to set up the query, 
> get it working the way I
> want it to, save the *QRYDFN, and use RTVQMQRY to generate the SQL.
>
> So, I am surprised to see that the generated SQL doesn't have any Join 
> clauses (?) but, instead,
> does the join via WHERE, i.e.:
>  FROM      PQPROD/PESTCCP T01,
>            PQPROD/PTBLCCP T02,
>            PQPROD/PJOBHDR T03
>  WHERE     T03.CMPNUM = T02.CMPNUM
>    AND     T01.CCPTYP = T02.TBLID
>    AND     T01.CCPNUM = T02.CCPNUM
>    AND     T01.JOBNUM = T03.JOBNUM
>    AND(    T01.JOBNUM = 'TACM0170'
>    AND     T02.CSTTYP = 'C')
>
> The join in WRKQRY