Re: Index not used with prepared statement

Guido Neitzer schrob:

> I have a performance problem with prepared statements (JDBC prepared
> statement).
>
> This query:
>
> PreparedStatement st = conn.prepareStatement("SELECT id FROM
> dga_dienstleister WHERE plz like '45257'");
>
> does use an index.
>
> This query:
>
>         String plz = "45257";
>         PreparedStatement st = conn.prepareStatement("SELECT id FROM
> dga_dienstleister WHERE plz like ?");
>         st.setString(1, plz);
>
> does NOT use an index.
>
> As it should in the end result in absolutely the same statement, the
> index should be used all the time.

I'm not perfectly sure, but since the index could only be used with a
subset of all possible parameters (the pattern for like has to be
left-anchored), I could imagine the planner has to avoid the index in
order to produce an universal plan (the thing behind a prepared
statement).

Is there a reason you are using the like operator at all? IMO using
the =-operator instead in your example should produce an "index-using
prepared statement".

HTH
Andreas
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