I understand, thanks. First: as I said in my previous post, the workhour_id was left behind by mistake and has since been removed.
So it seems that I can ommit the distinct completely and just use the query in it's simpelest form, like this: select employee_id, begindate as date from workhour UNION select employee_id, enddate as date from workhour And I would get a list of all dates (as well begin- as enddates) where a date can occure only once with each employee? Altough I didn't start this thread I'm learing some usefull things here, so some thanks to the people who replied (and started the thread) are in place here. Kind regards, Stijn Vanroye > -----Original Message----- > From: Stephan Szabo [mailto:[EMAIL PROTECTED] > Sent: maandag 17 mei 2004 17:01 > To: Stijn Vanroye > Cc: [EMAIL PROTECTED]; Edmund Bacon > Subject: Re: [SQL] a wierd query > > On Mon, 17 May 2004, Stijn Vanroye wrote: > > > Are you sure about that Edmund? > > > > I have the following query: > > select distinct on (task_id, date) task_id, > workhour_id, date from > > ( > > select task_id, workhour_id, begindate as date from workhour > > UNION > > select task_id, workhour_id, enddate as date from workhour > > )as dist1 > > This gets you first rows distincted by task_id, workhour_id and date > and then only rows distincted by task_id and date (and an > unpredictable > workhour_id). > > > if I use the query without the top level select, like this: > > select task_id, workhour_id, begindate as date from workhour > > UNION > > select task_id, workhour_id, enddate as date from workhour > > This gets rows distincted by task_id, workhour_id and date. > ---------------------------(end of broadcast)--------------------------- TIP 5: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faqs/FAQ.html
