That makes sense. Thanks! On Mon, Jun 25, 2012 at 12:52 PM, David Johnston <pol...@yahoo.com> wrote:
> On Jun 24, 2012, at 22:19, Excite Holidays <ehte...@gmail.com> wrote: > > > Hi, > > > > I have been making some test with EXISTS and I found I case that I do > not understand too well: > > > > CREATE TABLE testing ( > > number_id serial, > > number1 integer, > > number2 integer > > ); > > INSERT INTO testing (number1, number2) VALUES (1,1),(1,2),(2,3); > > > > SELECT * > > FROM testing > > WHERE EXISTS (SELECT 1 FROM testing WHERE testing.number_id = number_id > AND number1 = 1); > > > > As far I understand the documentation the select query should return row > 1 and 2, but it is returning 1, 2 and 3. > > > > Why is this happening ? > > > > PS_ PostgreSQL 9.1.1 on i686-pc-linux-gnu, compiled by gcc (Debian > 4.3.2-1.1) 4.3.2, 32-bit > > > > Regards, > > Ruben > > > > When you reference the same table in multiple locations you really should > give one of them an alias. > > In this case the non-table prefix number_id is resolving to the table > inside the exists so you basically get (... WHERE TRUE and number1 = 1) in > the sub-select and thus all rows are returned from the outer table (because > the query inside the exists is no longer linked to the outer query). As > long as at least one record is returned by the standalone query all records > will be selected in the outer query. If no records are returned by the > inner query then none will be returned by the outer. Without the linkage > you can never have a result that is a subset of the outer table. > > > David J.
