On Mon, 11 Aug 2003, Gary Stainburn wrote: > I don;t know if it's cos it's Monday or what, but I can't see what's wrong > here. > > I've got two tables, turns which holds a turn number, a task, and where > appropriate a link to a loco. The select below works but only shows those > tasks where a loco is involved.: > > select r.rtid, concat(r.rcid::text || ' on ' || l.lnumber::text) as task > from rides r, loco_dets l where r.rlid = l.lid group by rtid;
I assume concat is an aggregate function? > > rtid | task > ------+--------------------------------------------- > 5 | G on 60007 > 6 | A on 75014, C on 75014, A on 75029, C on 75029 > 7 | C on 4277, A on 44767, C on 44767 > 8 | A on 30926, C on 30926, G on 60532 > 9 | A on 30926, C on 30926, A on 75014, C on 75014 > 10 | F on 2392, F on 75029, L on 75029 > 11 | A on 44767, C on 44767, A on 75029 > > However, when I tried to change this to using an outer join I'm getting stuck. > Can anyone see my stumbling point, which I think is to do with the condition > part of the case statement. Do I need to do that in a sub-select first or is > there an alternative? > > =# select r.rtid, > -# case when r.rlid > 0 then > -# concat(r.rcid::text || ' on ' || l.lnumber::text) > -# else > -# r.rcid::text > -# end as task > -# from rides r > -# left outer join loco_dets l on r.rlid = l.lid > -# group by rtid > -# order by rtid > -# ; > ERROR: Attribute r.rlid must be GROUPed or used in an aggregate function Something like this might work: select r.rtid, concat(r.rcid::text || coalesce( ' on ' || l.lnumber::text,'')) as task from rides r left outer join loco_dets l on r.rlid=l.lid group by rtid order by rtid; IIRC, SQL99 has a complicated way of defining dependant columns for group by but SQL92 only allows you to use the columns that are grouped outside of an aggregate. In general, if r.rlid is >0 in some cases and <0 in others for a particular group, what would the query do? You might be able to show that it doesn't happen, but the system isn't quite that bright. ;) ---------------------------(end of broadcast)--------------------------- TIP 4: Don't 'kill -9' the postmaster
