Tom Lane <tgl@sss.pgh.pa.us> wrote:
John Sales writes:
> By doing this, I'm hoping that the query optimizer is smart enough to see that if a query comes in and requests only the six columns (that are in the narrower table) that PostgreSQL won't have to load the wider table into the buffer pool, and thereby actually have to only access about 10% the amount of disk that it presently does.
> Is this a sound theory?
No. It still has to touch the second table to confirm the existence of
rows to join to.
regards, tom lane
Good point..
What if I made the second table optional using an outer join, so as not to imply the existance of rows in the "wide" table?
thanks
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