Thread: Single row tables
Hi, with what constraint or how can I ensure that one of my tables has exact one record or 0..1 records?
I suppose you could put a check constraint that forces a single value on a column with a unique index? Or an insert triggerthat always inserts the same value into a unique field. Out of curiosity, why do you need to do this? Dmitri -----Original Message----- From: pgsql-sql-owner@postgresql.org [mailto:pgsql-sql-owner@postgresql.org] On Behalf Of KÖPFERL Robert Sent: Tuesday, January 11, 2005 9:46 AM Cc: pgsql-sql@postgresql.org Subject: [SQL] Single row tables Importance: High Hi, with what constraint or how can I ensure that one of my tables has exact one record or 0..1 records? ---------------------------(end of broadcast)--------------------------- TIP 7: don't forget to increase your free space map settings
Also I thought of an UNIQUE constraint on a column with =const constraint. But .... It's for global configuration data that exists only once. Making a key value thing was to weak typed for my taste. > -----Original Message----- > From: Dmitri Bichko [mailto:dbichko@genpathpharma.com] > Sent: Dienstag, 11. Jänner 2005 15:50 > To: KÖPFERL Robert > Cc: pgsql-sql@postgresql.org > Subject: RE: [SQL] Single row tables > > > I suppose you could put a check constraint that forces a > single value on a column with a unique index? Or an insert > trigger that always inserts the same value into a unique field. > > Out of curiosity, why do you need to do this? > > Dmitri > > -----Original Message----- > From: pgsql-sql-owner@postgresql.org > [mailto:pgsql-sql-owner@postgresql.org] On Behalf Of KÖPFERL Robert > Sent: Tuesday, January 11, 2005 9:46 AM > Cc: pgsql-sql@postgresql.org > Subject: [SQL] Single row tables > Importance: High > > > Hi, > > with what constraint or how can I ensure that one of my > tables has exact one record or 0..1 records? > > ---------------------------(end of > broadcast)--------------------------- > TIP 7: don't forget to increase your free space map settings >
On Tuesday 11 January 2005 17:45, KÖPFERL Robert wrote: > Hi, > > with what constraint or how can I ensure that one of my tables has exact > one record or 0..1 records? A trigger procedure BEFORE INSERT would help you. And a column type with only one possible field value would help you if you define UNIQUE INDEX on a field of this (user-defined) type.