Re: reducing number of ANDs speeds up query

Hi and thank you for your notes!

> You really ought to include the output of EXPLAIN ANALYZE in cases such as these (if it doesn't already point you to
theculprit). 

I'll do so, it takes quite long...

> Most likely you'll find that the last condition added a sequential scan to the query plan,

Exactly! EXPLAIN says so.

> which can have several causes/reasons. Are the estimated #rows close to the actual #rows?

Yes, this is the problem. I read that in such cases indexes are not read. However if the previous conditions are
executedfirst, the result is zero or just a few rows and there is no need seq scan the whole values column. 

> Is b.value indexed?

No, because it contains too long values for indexing.

> How selective is the value you're matching it against (is it uncommon or quite common)? Etc, etc.

Zero to a few.

> Meanwhile, it looks like most of your AND's are involved in joining tables a and b. Perhaps it helps to use an
explicitjoin instead of an implicit one? 

I am not quite sure what this means, but will read about it.

There were 2 more suggestions, I'll try now everything and write back.

Thank you very much for your help!
T.