Re: partial indexes not used on parameterized queries?

Hi Simon,

are you sure this has not been changed? I'm pretty sure my code worked a
while ago. We are using Perl DBD::Pg on the client side and almost never
pass parameters inside the SQL string for security reasons. I can't say
if it broke from 8.0 -> 8.1 for us or in one of the minor 8.1 releases.

In any case I would see this as a security problem because you cannot
control sql code injection easily (as with using DBD::Pg) if you have to
pass parameters in the SQL string to use partial indexes.

Regards,

Dirk

Simon Riggs wrote:
> On Mon, 2006-07-10 at 12:22 +0200, Dirk Lutzebäck wrote:
>
>
>> we are using postgresql 8.1.4 and found that partial indexes are not
>> being used when the query is run using parameters, eg. in a function.
>> When running the same query with arguments passed in the query string
>> partial indexes are being used.
>>
>
>
>> Any clues? Has this behaviour changed for a while?
>>
>
> No, it's always worked like this.
>
> The index can only be used if we know at plan time that the index
> predicate is true for all times that the query is executed. We cannot
> know this for the exact query and index combination you have requested.
> If we acted differently, your query would return the wrong answer in
> some circumstances.
>
> I can't find anything in the manual that explains this distinction.
>
> Here's an example that explains this more easily:
>
> If your index looked like this
>
> CREATE INDEX c_6000_index ON consumption (voi)
> WHERE
> code > 5000
> AND val1 IS NULL;
>
> and your query like this
>
> UPDATE c
> SET val1=1784
> WHERE
> ( code > 6000
> AND val1 IS NULL )
> AND code = ?
> AND voi = '1923328-8-0-0';
>
> ...then the index could be used, because the index predicate is implied
> by part of the query clause for all values of the parameter.
>
> So its best to look for some other static definition of the index.
>
> I'll submit a doc patch.
>
>

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*Dirk Lutzebäck* <lutzeb(at)aeccom(dot)com> Tel +49.30.5362.1635 Fax .1638
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