Yi Zhao wrote:
> I want to get the only 2 rows(limit or random) if the column "b" have
> the same value. so, the result of the above is
> a | b
> ---+---
> X | A
> X | A
> D | B
> H | B
> P | C
>
> how to do that, thanks all!
>
>
I don't understand what you want based on your description and your
example results. What do you mean by "if the column `b' have the same
value" ?
By the way, when you're posting this kind of question it's really
helpful to send SQL code to set up your test environment. For example,
if you had sent:
CREATE TABLE ab (a text, b text);
INSERT INTO ab (a,b) VALUES
('X','A'),('X','B'),('Y','A'),('D','B'),('H','B'),('E','B'),('D','B'),('P','C');
... then it would've saved the hassle of assembling a test table.
--
Craig Ringer
