Thread: sub-sel/group problem
Hi folks, 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.lidgroup by rtid; 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 on75014, 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 =# -- Gary Stainburn This email does not contain private or confidential material as it may be snooped on by interested government parties for unknown and undisclosed purposes - Regulation of Investigatory Powers Act, 2000
On Monday 11 August 2003 11:24 am, Gary Stainburn wrote: > Hi folks, > > 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.: > [snip] Having re-read my email and had another go, I've opted for the sub-select approach, and come up with: select rtid, concat(task) from (select rtid, case when r.rlid > 0 then 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)r group by rtid order by rtid ; Can anyone see any problems with this, or come up with a better approach? -- Gary Stainburn This email does not contain private or confidential material as it may be snooped on by interested government parties for unknown and undisclosed purposes - Regulation of Investigatory Powers Act, 2000
> > 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; > Looks like another implicit FROM clause mystery. Try ... GROUP BY r.rtid ; The same goes for the JOIN. Regards, Christoph
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. ;)
> Hi folks,
>
> 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;
>
> 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
> =#
Watch out.
When using outer joins you get NULL values.
some_text || NULL = NULL (always)
Try this:
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 r.rtid
order by r.rtid
Regards,
Tomasz Myrta