From: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
---|---|
To: | "Thomas F(dot) O'Connell" <tfo(at)sitening(dot)com> |
Cc: | pgsql-docs(at)postgresql(dot)org |
Subject: | Re: FAQ -- Index usage/speed |
Date: | 2004-08-31 19:05:54 |
Message-ID: | 200408311905.i7VJ5sv16159@candle.pha.pa.us |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-docs |
Yes, 4.8 would be the right spot. Not sure why we got so many reports
recently though.
However, with this fixed in 8.0, it probably isn't worth adding to the
FAQ.
---------------------------------------------------------------------------
Thomas F. O'Connell wrote:
> Bruce,
>
> Considering the activity on the lists (at least recently and, I think,
> historically) about postgres not casting (usually integer) constant
> values across types, could there be a mention of this made in the FAQ?
> It seems like a logical case for inclusion under 4.8:
>
> http://www.postgresql.org/docs/faqs/FAQ.html#4.8
>
> I was thinking something like the following:
>
> Also note that 7.x versions of postgres will not automatically cast
> constant data in certain queries such that an index would be used. For
> example, if you have the following:
>
> CREATE TABLE index_breaker (
> bigintcol int8 primary key
> some_data text
> );
>
> The following query is liikely to perform a sequential scan:
>
> SELECT some_data FROM index_breaker WHERE bigintcol = 42;
>
> postgres will interpret the constant value as a basic int and will thus
> not use the index (implicitly created by the primary key) on the
> bigintcol column.
>
> There are some workarounds for this issue [per Tom Lane]:
>
> 1. Always quote your constants:
>
> ... WHERE bigintcol = '42';
>
> Similarly, constants can be explicitly cast:
>
> ... WHERE bigintcol = int8( 42 )
>
> 2. Use a prepared statement:
>
> PREPARE foo(bigint) AS ... WHERE bigintcol = $1;
> EXECUTE foo(42);
>
> 3. Use parameterized statements in extended-query mode (essentially the
> same idea as #2, but at the protocol level). This doesn't help for
> pure SQL scripts, but is very workable when coding against libpq or
> JDBC. Among other things it gets you out of worrying about SQL
> injection attacks when your parameter values come from untrusted
> sources.
>
>
> Technical improvements to wording are welcome. But I think this is
> worth adding to the docs somewhere.
>
> Thanks!
>
> -tfo
>
--
Bruce Momjian | http://candle.pha.pa.us
pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 359-1001
+ If your life is a hard drive, | 13 Roberts Road
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073
From | Date | Subject | |
---|---|---|---|
Next Message | Thomas F.O'Connell | 2004-08-31 19:12:30 | Re: FAQ -- Index usage/speed |
Previous Message | Thomas F.O'Connell | 2004-08-31 16:30:45 | FAQ -- Index usage/speed |