Question

I read on SO that join is performed before where so I was wondering if it is (always) a good idea to perform a join like so:

SELECT * FROM 
    (SELECT * FROM tbl_1 WHERE field = 'the_value') t
    JOIN tbl_2 USING (joinable_field)

instead of the usual

SELECT * FROM tbl_1 t1 JOIN tbl_2 t2 USING (joinable_field)
WHERE t1.field = 'the_value'

Answer 1

With this, you are restricting the execution and evaluation order. t must be created first (maybe “on the fly”, maybe physially on disk), and tbl_2 is joined in.

In your concrete case, this shouldn’t hurt, however. But I cannot see a benefit, either.