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Re: Can't use WITH in a PERFORM query in PL/pgSQL?

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Bruce Momjian <bruce(at)momjian(dot)us>
Cc: depstein(at)alliedtesting(dot)com, pgsql-bugs(at)postgresql(dot)org, pgagarinov(at)alliedtesting(dot)com, vshahov(at)alliedtesting(dot)com
Subject: Re: Can't use WITH in a PERFORM query in PL/pgSQL?
Date: 2011-10-19 12:36:26
Message-ID: CA+TgmoazonH3XsKwCO1-MSpd+YnT48TpzcHjEJRJQDjkY1Y-AA@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-bugs
On Tue, Sep 6, 2011 at 1:43 PM, Bruce Momjian <bruce(at)momjian(dot)us> wrote:
> Well, this problem isn't isolated to WITH queries:
>
>        test=> do
>        $$begin
>        perform(
>        select 1 UNION ALL select 1
>        );
>        end$$;
>        ERROR:  more than one row returned by a subquery used as an expression
>
>        test=> do
>        $$begin
>        perform(
>        select relname from pg_class
>        );
>        end$$;
>        ERROR:  more than one row returned by a subquery used as an expression
>

Based on previous experience with PL/pgsql, my understanding is that
PL/pgsql basically replaces "perform" with "select" to get the query
that it actually runs.  You'd get the same error from:

rhaas=# select (select relname from pg_class);
ERROR:  more than one row returned by a subquery used as an expression

I've never really liked this behavior, but I don't have a clear idea
what to do about it.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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