Обсуждение: Query optimizer & prepared statements

If x is an integer column with an index, then

     select ...
     from T
     where x > 1

and

     select ...
     from T
     where x > 1000000000

could be optimized differently. So how is optimization done for a prepared
statement containing a variable, e.g.

     select ...
     from T
     where x > $1

Jack Orenstein

>
>    select ...
>    from T
>    where x > $1
>

prepare testy_prepare(int) as select * from T where x = $1;

execute testy_prepare(4);

Follow the docs :)
http://www.postgresql.org/docs/8.1/interactive/sql-prepare.html


--
              Emanuel Calvo Franco
ArPUG [www.arpug.com.ar] / AOSUG Member
        www.emanuelcalvofranco.com.ar

Jack Orenstein wrote:
> If x is an integer column with an index, then
>
>     select ...
>     from T
>     where x > 1
>
> and
>
>     select ...
>     from T
>     where x > 1000000000
>
> could be optimized differently. So how is optimization done for a
> prepared statement containing a variable, e.g.
>
>     select ...
>     from T
>     where x > $1

http://www.postgresql.org/docs/current/static/sql-prepare.html#AEN58703
explains this.

If your parameter is a unique key, then you won't see any difference. If
your parameter is a non-unique key, there may be differences depending
on your data/distribution etc.

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