$PostgreSQL: pgsql/src/backend/optimizer/README,v 1.49 2009/02/27 22:41:37 tgl Exp $

$PostgreSQL: pgsql/src/backend/optimizer/README,v 1.50 2009/07/21 02:02:44 tgl Exp $

Optimizer

=========

!= (A leftjoin B on (Pab)) join C on (Pbc)

SEMI joins work a little bit differently. A semijoin can be reassociated

into or out of the lefthand side of another semijoin,but not into or out

of the righthand side. Likewise, an inner join, left join, or antijoin

can be reassociated into or out of the lefthand side of a semijoin, but

not into or out of the righthand side.

into or out of the lefthand side of another semijoin,left join, or

antijoin, but not into or outof the righthand side. Likewise, an inner

join, left join, or antijoincan be reassociated into or out of the

lefthand side of a semijoin, butnot into or out of the righthand side.

ANTI joins work approximately like LEFT joins, except that identity 3

fails if the join to C is an antijoin (even if Pbc is strict, and in

if (bms_overlap(left_rels,otherinfo->syn_righthand))

{

if (bms_overlap(clause_relids,otherinfo->syn_righthand)&&

(jointype==JOIN_ANTI||

(jointype==JOIN_SEMI||jointype==JOIN_ANTI||

!bms_overlap(strict_relids,otherinfo->min_righthand)))

{

min_lefthand=bms_add_members(min_lefthand,

{

if (bms_overlap(clause_relids,otherinfo->syn_righthand)||

!otherinfo->lhs_strict||otherinfo->delay_upper_joins)

{