In response to Yi Zhao : > thanks Ringer. > my mean is that: > I want less than 2 rows which have the same value of column "b"! > > for example, there is 3 columns have the same value "A", > X | A > X | A > Y | A > I want my result have two of them. I think, you are searching for DISTINCT: test=# create table foo (a text, b text); CREATE TABLE test=*# copy foo from stdin; Enter data to be copied followed by a newline. End with a backslash and a period on a line by itself. >> a a >> a a >> b a >> \. test=*# select distinct a,b from foo; a | b ---+--- a | a b | a (2 rows) Please, no silly top-posting. A: Because it messes up the order in which people normally read text. Q: Why is top-posting such a bad thing? A: Top-posting. Q: What is the most annoying thing in e-mail? Andreas -- Andreas Kretschmer Kontakt: Heynitz: 035242/47150, D1: 0160/7141639 (mehr: -> Header) GnuPG-ID: 0x3FFF606C, privat 0x7F4584DA http://wwwkeys.de.pgp.net -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
