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Re: BUG #6612: Functions can be called inside CHECK statements

From: "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov>
To: <atrigent(at)ccs(dot)neu(dot)edu>,"Greg Stark" <stark(at)mit(dot)edu>
Cc: <pgsql-bugs(at)postgresql(dot)org>
Subject: Re: BUG #6612: Functions can be called inside CHECK statements
Date: 2012-04-25 15:06:48
Message-ID: 4F97CCB80200002500047332@gw.wicourts.gov (view raw or flat)
Thread:
Lists: pgsql-bugs
Greg Stark <stark(at)mit(dot)edu> wrote:
 
> Only IMMUTABLE functions can be used in CHECK constraints.
> It's a feature that expressions including subqueries are
> automatically detected as not being immutable and automatically
> barred.
 
It doesn't look like that to me:
 
test=# create function xxx() returns text volatile language plpgsql
as $$ begin return 'xxx'; end; $$;
CREATE FUNCTION
test=# create table x (id int not null primary key, val text check
(val <> xxx()));
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index
"x_pkey" for table "x"
CREATE TABLE
test=# insert into x values (1, 'aaa');
INSERT 0 1
test=# insert into x values (2, 'xxx');
ERROR:  new row for relation "x" violates check constraint
"x_val_check"
DETAIL:  Failing row contains (2, xxx).
 
Perhaps you're thinking of function usage in index definitions?

A CHECK constraint using a volatile function is potentially valid
and useful, IMO.  Think about a column which is supposed to record
the moment of an event which has occurred.  It could make sense to
ensure that the timestamptz value is < now();  On the other hand, an
index entry based on now() is clearly a problem.
 
Otherwise I agree with your response -- this is clearly *not* a bug.
 
-Kevin

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