2010/9/9 Martín Marqués <martin.marques@xxxxxxxxx>: > I was looking at rows in a table which are not referenced from another > and found some discrepencies. > > These are the queries (with results): > > SELECT * from grupo_concursantes where codigo NOT IN (SELECT grupo > FROM concursantes); > codigo | numero | evento | escuela > --------+--------+--------+--------- > (0 filas) > > SELECT g.* FROM grupo_concursantes g left outer join concursantes c on > (g.codigo=c.grupo) > where c.codigo IS NULL; > codigo | numero | evento | escuela > --------+--------+--------+--------- > 25 | 1 | 1 | 69331 > 33 | 2 | 1 | 60233 > 53 | 2 | 1 | 60490 > 64 | 6 | 1 | 68861 > 73 | 1 | 1 | 69220 > (5 filas) > > Why aren't the 5 rows from the second query in the first? These are doing different things. The first one is matching rows in grupo_concursantes where codigo doesn't appear in concursantes.grupo (and bear in mind, NULL concursantes.grupo values won't match this evaluation) . The second one is returning every instance of concursantes where where they *do* match, but where concursantes.codigo is NULL, which isn't mentioned in the first query. I'm wondering that if you used * instead of g.* in the second query whether you'd get NULLs returned in the grupo column. -- Thom Brown Twitter: @darkixion IRC (freenode): dark_ixion Registered Linux user: #516935 -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
