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Re: Prepare Statement

From: Kris Jurka <books(at)ejurka(dot)com>
To: Jie Liang <jie(at)stbernard(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-sql(at)postgresql(dot)org,pgsql-jdbc(at)postgresql(dot)org
Subject: Re: Prepare Statement
Date: 2004-06-17 22:25:54
Message-ID: Pine.BSO.4.56.0406171720310.16501@leary.csoft.net (view raw or flat)
Thread:
Lists: pgsql-jdbcpgsql-sql

On Thu, 17 Jun 2004, Jie Liang wrote:

> Kris,
> You are right, I modified that piece of code a little bit,
> CallableStatement stmt = conn.prepareCall("{?=call chr(?)}");
> Then my log file were:
> Select * from chr(65) as result;
> Select * from chr(66) as result;
> ......
> However, if I use:
> PrepareStatement stmt = conn.prepareStatement("SELECT chr(?)");
> Then my log file are same as yours.i.e. it use PREPARE and EXECUTE.
> 
> So, I am getting confusion.
> I think CallableStatement is extended from PrepareStatement, it should
> have same behaviou.
> 

What's happening here is that you can only use prepared statements for 
certain operations.  You can't for example prepare a CREATE TABLE 
statement.  The driver examines the query to see if it is valid for 
preparing and I believe the problem here is that with a callable statement 
it is examinging the query with "call" before it is transformed to a 
SELECT, so it doesn't recognize it as a preparable.  This looks like a bug 
to me.

Kris Jurka


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