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
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