efficient query help please.

[SDB]

hmmm.. ok, option a) thank you, that's what I have now.

option b) isn't quite what I meant..

What i meant is...

if I already have a query such as :

SELECT threadid from specialtable ....

what's the most efficient way include a column in the returned results which establishes whether userid x has posted in that thread.

So I would end up with results with columns [specialtable.threadid] and [useridhasposted or useridpostcount or similar]

Thanks in advance

Simon