On Jul 5, 2012, at 3:51 PM, Tom Lane wrote: > Steven Schlansker <steven@xxxxxxxxxxxx> writes: >> Why is using an OR so awful here? > > Because the OR stops it from being a join (it possibly needs to return > some rows that are not in the semijoin of the two tables). > >> Why does it pick a sequential scan? Is this an optimizer bug > > No. It can't transform OR into a UNION because the results might not > be the same. I assume you don't care about removal of duplicates, or > have some reason to know that there won't be any ... but the planner > doesn't know that. > Thanks for the insight here. It still seems unfortunate that it picks a sequential scan -- but if there really is no more efficient way to do this, I will just rewrite the query. Steven -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
