Received: from makus.postgresql.org (makus.postgresql.org [98.129.198.125]) by mail.postgresql.org (Postfix) with ESMTP id 4C20884FED3 for ; Tue, 24 Jul 2012 23:23:04 -0300 (ADT) Received: from [210.83.216.99] (helo=edgesoft.cn) by makus.postgresql.org with esmtp (Exim 4.72) (envelope-from ) id 1StrFf-0005Ed-AK for pgsql-admin@postgresql.org; Wed, 25 Jul 2012 02:23:04 +0000 Received: from [10.18.27.77] (unknown [10.18.27.77]) (Authenticated sender: wangqi@edgesoft.cn) by mail.edgesoft.cn (Postfix) with ESMTPA id 584B7810F for ; Wed, 25 Jul 2012 10:22:45 +0800 (CST) Message-ID: <500F5870.8010400@edgesoft.cn> Date: Wed, 25 Jul 2012 10:22:40 +0800 From: wangqi User-Agent: Mozilla/5.0 (Windows NT 5.1; rv:13.0) Gecko/20120614 Thunderbird/13.0.1 MIME-Version: 1.0 To: pgsql-admin@postgresql.org Subject: about select use random Content-Type: text/plain; charset=GB2312 Content-Transfer-Encoding: quoted-printable X-Host-Lookup-Failed: Reverse DNS lookup failed for 210.83.216.99 (failed) X-Pg-Spam-Score: 1.6 (+) X-Archive-Number: 201207/71 X-Sequence-Number: 39788 Hi everyone =A1=F6SQL-1 CREATE TABLE wk_mclid1( id1 integer , PRIMARY KEY(id1) ); =A1=F6SQL-2 INSERT INTO wk_mclid1(id1) VALUES(1),(2),(3),(4),(5),(6),(7),(8),(9),(10) GO =A1=F6SQL-3 select * from wk_mclid1 where id1=3D (round((random() * (10-1))::integer) + 1)::integer; When we excute SQL-3,sometimes the result was 0 record or more than 1 record. Why? =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D select * from wk_mclid1 where id1=3D (round((random() * (10-1))::integer) + 1)::integer; id1 ------ 9 =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D select * from wk_mclid1 where id1=3D (round((random() * (10-1))::integer) + 1)::integer; id1 ------ 4 6 7 =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D select * from wk_mclid1 where id1=3D (round((random() * (10-1))::integer) + 1)::integer; id1 ------ 0 record(s) selected [Fetch MetaData: 94/ms] [Fetch Data: 0/ms] =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D thanks!