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