Re: [SQL] LEFT JOIN ...

The Hermit Hacker <scrappy@hub.org> writes:
>       FROM note_links nl, notes n LEFT JOIN calendar c ON (n.nid = c.nid)
>       WHERE (n.type = 'A' OR n.type = 'N' OR n.type = 'H' OR n.type = 'C')
>             AND (nl.id = 15748 AND contact_lvl = 'company')
>             AND n.nid = nl.nid
>       ORDER BY start DESC;

> Is there some way to write the above so that it evaluates:
> first, so that it only has to do the LEFT JOIN on the *one* n.nid that is
> returned, instead of the 86736 that are in the table?

Try adding ... AND n.nid = 15748 ...  to the WHERE.  It's not very
bright about making that sort of transitive-equality deduction for
itself...
        regards, tom lane