Tom Lane wrote:
Rich Doughty <rich@xxxxxxxxxx> writes:
However, the following query (which i believe should be equivalent)
SELECT *
FROM
tokens.ta_tokenhist h INNER JOIN
tokens.ta_tokens t ON h.token_id = t.token_id LEFT JOIN
tokens.ta_tokenhist i ON t.token_id = i.token_id AND
i.status = 'issued' LEFT JOIN
tokens.ta_tokenhist s ON t.token_id = s.token_id AND
s.status = 'sold' LEFT JOIN
tokens.ta_tokenhist r ON t.token_id = r.token_id AND
r.status = 'redeemed'
WHERE
h.sarreport_id = 9
;
No, that's not equivalent at all, because the implicit parenthesization
is left-to-right; therefore you've injected the constraint to a few rows
of ta_tokenhist (and therefore only a few rows of ta_tokens) into the
bottom of the LEFT JOIN stack. In the other case the constraint is at
the wrong end of the join stack, and so the full view output gets formed
before anything gets thrown away.
Some day the Postgres planner will probably be smart enough to rearrange
the join order despite the presence of outer joins ... but today is not
that day.
thanks for the reply.
is there any way i can achieve what i need to by using views, or should i
just use a normal query? i'd prefer to use a view but i just can't get round
the performance hit.
--
- Rich Doughty
