On Wed, Feb 23, 2005 at 19:33:07 +0100, KÖPFERL Robert <[EMAIL PROTECTED]> wrote: > > Otherwise you can treat this as a subselect and suround it with another > select. > > Like > select * from (<here goes your ex.>) order by orderno;
That is still a bad idea in this case. He will end up scanning the table three times to pick up the three days and there will be a sort for each union to remove duplicates (which there shouldn't be if orderno is a candidate key). > > C:\> -----Original Message----- > C:\> From: Bruno Wolff III [mailto:[EMAIL PROTECTED] > C:\> Sent: Mittwoch, 23. Februar 2005 18:20 > C:\> To: WeiShang > C:\> Cc: pgsql-sql@postgresql.org > C:\> Subject: Re: [SQL] VIEW / ORDER BY + UNION > C:\> > C:\> > C:\> On Thu, Feb 17, 2005 at 23:46:59 +0800, > C:\> WeiShang <[EMAIL PROTECTED]> wrote: > C:\> > Hi, I have created a view like this : > C:\> > > C:\> > CREATE VIEW v1 AS (SELECT orderno,weekday,time FROM t1,t2 where > C:\> > t1.orderno=t2.orderno); > C:\> > > C:\> > if I create a SQL statment: > C:\> > > C:\> > (SELECT orderno FROM v1 WHERE weekday='MON' ORDER BY orderno) > C:\> > UNION > C:\> > (SELECT orderno FROM v1 WHERE weekday='WED' ORDER BY orderno) > C:\> > UNION > C:\> > (SELECT orderno FROM v1 WHERE weekday='FRI' ORDER BY orderno); > C:\> > > C:\> > Will the whole result will be sorted by the field orderno? > C:\> > C:\> If this isn't a made up example, you don't want to do this. You > C:\> should use IN or OR to select records corresponding to the days > C:\> of interest and then use ORDER BY to select the ordering. > C:\> > C:\> ---------------------------(end of > C:\> broadcast)--------------------------- > C:\> TIP 7: don't forget to increase your free space map settings > C:\> > > ---------------------------(end of broadcast)--------------------------- > TIP 1: subscribe and unsubscribe commands go to [EMAIL PROTECTED] ---------------------------(end of broadcast)--------------------------- TIP 6: Have you searched our list archives? http://archives.postgresql.org
