Hi to all,
DB2 seems to do a SORT before every GROUP. At least if I look at the query plan of -
-- connected to the sample db
-
SELECT WORKDEPT, SUM(SALARY)
-
FROM EMPLOYEE
-
GROUP BY WORKDEPT
-
a SORT is performed before GRPBY. I can imagine that it's necessary, but why?
Greetings, Martina.
3  2172 
Hi to all,
DB2 seems to do a SORT before every GROUP. At least if I look at the query plan of
-
-- connected to the sample db
-
SELECT WORKDEPT, SUM(SALARY)
-
FROM EMPLOYEE
-
GROUP BY WORKDEPT
-
a SORT is performed before GRPBY. I can imagine that it's necessary, but why?
Greetings, Martina.
Hi, how did you check that a sort is performed before the groupby?
I use Visual Explain within the Command Center.
NeoPa 32,556
Expert Mod 16PB
This is quite standard in SQL generally.
The engine has to process through the input somehow.
If it can process through by a relevant key then it will - otherwise it has to sort before it can tell if the next record is part of 'this' group or the beginning of the next.
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