I almost always alias my tables by default with something short (Usually 1 - 3 characters), but not my subselects for an in list. In this case I would do d1, d2, ps, and p for the different tables. I then do my best to use the same alias in all my queries. I am also big on formatting the SQL here is how I would write what you have for readability
INNER
JOIN partner_share AS ps
JOIN partner_share AS ps
INNER
JOIN partner AS p
JOIN partner AS p
ON ps.partner_id = p.partner.id
WHERE p.team_id = 12345
AND (ps.type = 1 AND d2.external_id IS NOT NULL
OR ps.type = 2 AND d2.external_id IS NULL)
)
WHERE p.team_id = 12345
AND (ps.type = 1 AND d2.external_id IS NOT NULL
OR ps.type = 2 AND d2.external_id IS NULL)
)
On Fri, Oct 4, 2013 at 5:59 AM, Ladislav Lenart <lenartlad@xxxxxxxx> wrote:
Hello.
I have a noob question about table aliases in SQL.
Suppose the following query:
SELECT *
FROM deal
WHERE
deal.id IN (
SELECT DISTINCT deal.id
FROM
deal
JOIN partner_share ON deal.id = partner_share.deal_id
JOIN partner ONshare.partner_id = partner.id
WHERE
partner.team_id = 12345
AND (
partner_share.type = 1 AND deal.external_id IS NOT NULL
OR partner_share.type = 2 AND deal.external_id IS NULL
)
)
As you can see, the IN (...) references the deal table too.
My questions:
* Should I alias one of the references to deal?
* The above query works the same both with and without an alias, so is it simply
a matter of taste / good practice?
* Where can I find more info about this, i.e. when the alias is mandatory and
when it is only a convenience? I've scanned through
http://www.postgresql.org/docs/9.1/static/queries-table-expressions.html
but it only mentions that subselect in FROM must have an alias. I would like to
know about IN (...) and EXISTS (...).
Thank you,
L.
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