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Conditional JOIN
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koslo
Member
posted
In Mainframe FOCUS. Trying to do a conditional JOIN. It seems to me that the purpose of using WHERE statements with the JOIN is to do more filtering right up front at JOIN time, even before the other WHERE statements in the query are tested.

We are accessing DB2 tables. When I look at the SQL generated by the conditional JOIN, the first thing I see is a cartesian product. SELECT ... FROM A, B. Even if this is filtered later, it CAN'T be FAST!! Am I doing something wrong or misunderstanding something?

Thanks,
Phyllis
 
Posts: 15 | Registered: May 17, 2004Report This Post
j.gross
Virtuoso
posted Hide Post
Perhaps WF cannot pass the WHERE condition in the join through to DB2.

What SQL is generated when you move the Where from the JOIN into the Table request?
 
Posts: 1925 | Location: NYC | In FOCUS since 1983 | Registered: January 11, 2005Report This Post
koslo
Member
posted Hide Post
When the WHERE statements all are in the TABLE request, the SQL picks up the JOIN as expected: SELECT ... from A, B, WHERE A.x = B.x AND ... But that isn't a "conditional JOIN". The conditional JOIN puts something other than equality right into the JOIN statement. When I do that, not only are the other WHERE filters ignored in the SQL, but so is the equality.

Thanks for considering this. I just wonder why conditional JOIN's don't seem to work at all.

Phyllis
 
Posts: 15 | Registered: May 17, 2004Report This Post
j.gross
Virtuoso
posted Hide Post
I wasn't suggesting that -- just wanted to rule out the possibility that WF has some reason for not passing your condition in SQL. Since you've ruled that out, sounds like a bug.

Open a case.
 
Posts: 1925 | Location: NYC | In FOCUS since 1983 | Registered: January 11, 2005Report This Post
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