Bugs item #2787448, was opened at 2009-05-05 20:52
Message generated for change (Comment added) made by stmane
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Category: SQL/Core
Group: MonetDB5 CVS Head
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Stefan de Konink (skinkie)
Assigned to: Niels Nes (nielsnes)
Summary: Better error message for count(*) vs order by

Initial Comment:
sql>select count(*) from way_tags, mytemp, mytemp2 where k= 'highway' and v = 
'unclassified' and way_tags.way = mytemp2.way and mytemp2.segment = mytemp.row 
order by mytemp2.way, mytemp2.segment;
!SELECT: no such column 'mytemp2.way'

It took me some while to figure out that count(*) didn't like order by.

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>Comment By: Stefan Manegold (stmane)
Date: 2009-05-05 23:23

Message:
AFAIR, the SQL standard required order by columns and/or expression to
occur in the projection list (select clause) of the query.
Basically, consider order by working on a subset of the projection list
(select clause) of the query.
A possible reason herefore is (IMHO) that otherwise (i.e., with not all
order by columns present in the result, implicit duplicate elimination
might drop tuples that have been used for sorting.
Then the error message is IMHO quite clear in your case: by the time order
by get's its turn, all columns are already projected away.

(Let alone that using order by in a query that is supposed to return a
single single-attribute tuple, i.e., a single value, does not seems to make
much sense, anyway ... ;-))


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