Conditional Join - join 1 tables 2 ways

Question

I have a set of (not very well normalised or relational) tables named PLAN, GROUP, PRODUCT CLIENT

Most have linkage i.e. PLAN -> CLIENT on clno GROUP to PRODUCT on PRODCD

However, the linkage between PLAN and GROUP is tricky. A plan has 2 field of interest GRPNO and PRODCD.

What I want to do is if GRPNO != 0 then join GROUP on GRPNO. However if GRPNO = 0 then I want to join GROUP on PRODCD.

The frustrating thing is that the fileds I want to return in my queries are the same across the board I just need to be able to vary the join, or join the same table twice.

The best I can come up with is 2 queries and merge them using datasets, or possibly using a union.

Is there a nifty way to do this in one select?

I should point out I am access Foxpro over ODBC to do this.

Thank you!

Answer 1

You can do:

JOIN GROUP AS G ON
(PL.GRPNO = 0 AND G.PRODCD = PL.PRODCD) OR
(PL.GRPNO !=0 AND G.GRPNO = PL.GRPNO)

However it would surprise me if this is faster than using UNION ALL.