Re: select where not exists returning multiple rows? - Mailing list pgsql-general

From Martijn van Oosterhout
Subject Re: select where not exists returning multiple rows?
Date
Msg-id 20111102131342.GA4968@svana.org
Whole thread Raw
In response to select where not exists returning multiple rows?  (Chris Dumoulin <chris@blaze.io>)
Responses Re: select where not exists returning multiple rows?  (Chris Dumoulin <chris@blaze.io>)
List pgsql-general
On Wed, Nov 02, 2011 at 07:22:09AM -0400, Chris Dumoulin wrote:
> And we're doing an insert like this:
> INSERT INTO Item (Sig, Type, Data) SELECT $1,$2,$3 WHERE NOT EXISTS
> ( SELECT NULL FROM Item WHERE Sig=$4)
>
> In this case $1 and $4 should always be the same.

FWIW, If they're always going to be the same, you can put that it the query,
like so:

INSERT INTO Item (Sig, Type, Data) SELECT $1,$2,$3 WHERE NOT EXISTS
( SELECT NULL FROM Item WHERE Sig=$1)

Saves a parameter.

> I don't see how it's possible to get duplicate rows here, unless
> maybe the "select where not exists" is somehow returning multiple
> rows.
> Any ideas what's going on here?

As pointed out by others, you don't say if it this is a race condition
between processes or if it always does this.

Have a nice day,
--
Martijn van Oosterhout   <kleptog@svana.org>   http://svana.org/kleptog/
> He who writes carelessly confesses thereby at the very outset that he does
> not attach much importance to his own thoughts.
   -- Arthur Schopenhauer

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