| From: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
|---|---|
| To: | Jean-Christian Imbeault <jc(at)mega-bucks(dot)co(dot)jp> |
| Cc: | pgsql-general <pgsql-general(at)postgresql(dot)org> |
| Subject: | Re: LIMIT: does it cause the query to find all matching sets |
| Date: | 2002-09-30 15:08:02 |
| Message-ID: | 200209301508.g8UF82615027@candle.pha.pa.us |
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| Lists: | pgsql-general |
Jean-Christian Imbeault wrote:
> Does using LIMIT cause query execution to stop as soon as the LIMIT
> number of matches have been found, or are *all* the matching rows found
> first and then the first LIMIT number are returned?
>
> Of course this would be for a query without and ORDER BY clause.
A query without ORDER BY is possible, and it will stop after it hits the
limit. Of course, without ORDER BY there is no way to know which rows
were returned.
Second, if you do use ORDER BY, LIMIT can sometimes use an index and not
have to execute the entire query, so yes, that optimization is in there.
--
Bruce Momjian | http://candle.pha.pa.us
pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 359-1001
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