From: | wangqi <wangqi(at)edgesoft(dot)cn> |
---|---|
To: | pgsql-admin(at)postgresql(dot)org |
Subject: | about select use random |
Date: | 2012-07-25 02:22:40 |
Message-ID: | 500F5870.8010400@edgesoft.cn |
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Thread: | |
Lists: | pgsql-admin |
Hi everyone
■SQL-1
CREATE TABLE wk_mclid1(
id1 integer ,
PRIMARY KEY(id1)
);
■SQL-2
INSERT INTO wk_mclid1(id1)
VALUES(1),(2),(3),(4),(5),(6),(7),(8),(9),(10)
GO
■SQL-3
select * from wk_mclid1 where id1= (round((random() * (10-1))::integer)
+ 1)::integer;
When we excute SQL-3,sometimes the result was 0 record or more than 1
record.
Why?
============================================================================================
select * from wk_mclid1 where id1= (round((random() * (10-1))::integer)
+ 1)::integer;
id1
------
9
============================================================================================
select * from wk_mclid1 where id1= (round((random() * (10-1))::integer)
+ 1)::integer;
id1
------
4
6
7
============================================================================================
select * from wk_mclid1 where id1= (round((random() * (10-1))::integer)
+ 1)::integer;
id1
------
0 record(s) selected [Fetch MetaData: 94/ms] [Fetch Data: 0/ms]
============================================================================================
thanks!
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