Does "group by" automatically guarantee "order by"?

sql database group-by database-agnostic
Tomas picture Tomas · Jan 26, 2015 · Viewed 14.1k times · Source

Does "group by" clause automatically guarantee that the results will be ordered by that key? In other words, is it enough to write:

select * 
from table
group by a, b, c

or does one have to write

select * 
from table
group by a, b, c
order by a, b, c

I know e.g. in MySQL I don't have to, but I would like to know if I can rely on it accross the SQL implementations. Is it guaranteed?

Answer

juergen d picture juergen d · Jan 26, 2015

group by does not order the data neccessarily. A DB is designed to grab the data as fast as possible and only sort if necessary.

So add the order by if you need a guaranteed order.

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