On Fri, Mar 9, 2012 at 8:15 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: > Antonin Houska <antonin.hou...@gmail.com> writes: >> For example: > >> SELECT * >> FROM a, b, func(a.i, b.j) as c, d >> WHERE a.i=b.j and b.j = d.k and c>1 > >> may become > >> SELECT * >> FROM a, b, <subquery> as c, d >> WHERE a.i=b.j and b.j = d.k and c>1 > >> where <subquery> is > >> SELECT func(a.i, b.j) >> FROM a,b >> WHERE a.i=b.j > > Um ... how do you get the subquery result rows to join to only the > correct rows of the other tables? This looks like an unconstrained join > to me, which is not what I believe the SQL spec for LATERAL to be, and > it doesn't seem especially useful either. (If a subquery could do what > people wanted, we'd not be hearing all the requests for LATERAL.)
I think LATERAL is intended as more or less an unconstrained nested loop with the lateral expression on the inner side, parameterized by value from the outer side. Typically it's a SRF. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
