Обсуждение: BUG #3891: Multiple UPDATE doesn't handle UNIQUE constraint correctly
The following bug has been logged online: Bug reference: 3891 Logged by: Adriaan van Os Email address: postgres@microbizz.nl PostgreSQL version: 8.2.4 Operating system: Mac OS X 10.5 Description: Multiple UPDATE doesn't handle UNIQUE constraint correctly Details: Suppose we have a table A with a UNIQUE column Name of type VARCHAR, a PRIMARY KEY record_id of type INT4 and the following records A record_id Name 1 X 2 Y Furthermore, we have a temporary table temp_A with a UNIQUE column Name of type VARCHAR, a PRIMARY KEY record_id of type INT4 and the following records temp_A record_id Name 1 Y 2 X Now, we update table A with values from temporary table temp_A doing something like UPDATE "A" SET "Name" = "temp_A"."Name" FROM "temp_A" WHERE "A".record_id = "temp_A".record_id This will cause a UNIQUE violation in de middle of the UPDATE statement, although after completion of the statement there is no such violation. Although deferred constraints are not yet implemented for Postgres, the docs at <http://www.postgresql.org/docs/8.2/static/sql-set-constraints.html> state: IMMEDIATE constraints are checked at the end of each statement. Apparently, this is not correct, as in the above example constraints are checked in the middle of a statement, rather than at the end. I feel the docs are right here and the software wrong. Sincerely, Adriaan van Os
Re: BUG #3891: Multiple UPDATE doesn't handle UNIQUE constraint correctly
От
Euler Taveira de Oliveira
Дата:
Adriaan van Os wrote: > This will cause a UNIQUE violation in de middle of the UPDATE statement, > although after completion of the statement there is no such violation. > This is not a bug. > Although deferred constraints are not yet implemented for Postgres, the docs > at <http://www.postgresql.org/docs/8.2/static/sql-set-constraints.html> > state: > But I forgot to read this: "Check and unique constraints are always effectively not deferrable." It's a known "problem" (TODO item). See Greg's elegant solution [1]. [1] http://people.planetpostgresql.org/greg/index.php?/archives/2006/06/10.html -- Euler Taveira de Oliveira http://www.timbira.com/
On Mon, Jan 21, 2008 at 08:17:47AM +0000, Adriaan van Os wrote: > > The following bug has been logged online: > > Bug reference: 3891 > Logged by: Adriaan van Os > Email address: postgres@microbizz.nl > PostgreSQL version: 8.2.4 > Operating system: Mac OS X 10.5 > Description: Multiple UPDATE doesn't handle UNIQUE constraint > correctly > Details: > > Suppose we have a table A with a UNIQUE column Name of type VARCHAR, a > PRIMARY KEY record_id of type INT4 and the following records > > A > record_id Name > 1 X > 2 Y > > Furthermore, we have a temporary table temp_A with a UNIQUE column Name of > type VARCHAR, a PRIMARY KEY record_id of type INT4 and the following > records > > temp_A > record_id Name > 1 Y > 2 X > > Now, we update table A with values from temporary table temp_A doing > something like > > UPDATE "A" SET "Name" = "temp_A"."Name" FROM "temp_A" WHERE "A".record_id = > "temp_A".record_id You can do something like FROM (SELECT * FROM "temp_A" ORDER BY record_id) AS "A" so it won't collide. Cheers, David. -- David Fetter <david@fetter.org> http://fetter.org/ Phone: +1 415 235 3778 AIM: dfetter666 Yahoo!: dfetter Skype: davidfetter XMPP: david.fetter@gmail.com Remember to vote! Consider donating to Postgres: http://www.postgresql.org/about/donate