On 3-2-2019 23:29, Gerlando Falauto wrote:
IMHO, adding the ORDER BY clause to query 1) above (i.e. query 2) should
ideally yield the exact same query plan.
In the end adding an ORDER BY clause on the exact same columns of the index
used to traverse the table, should be easily recognizable.
Knowing absolutely nothing about the internals though, I have no idea
whether this particular use case has been overlooked, or it would just be
unfeasible to handle it.
In SQL, when doing a SELECT, the order of the results is undetermined
(by definition).
If you want/need to results to be ORDERed, you need to add 'ORDER BY'.
This will always show as an extra step in your QUERY PLAN.
One can never know (for sure) if the output of this is in the correct order:
CREATE TABLE test(i primary key);
INSERT INTO test values(4);
INSERT INTO test values(2);
INSERT INTO test values(3);
INSERT INTO test values(1);
SELECT i FROM test;
4
2
3
1
To 'know' it is in the correct order one has to define an ORDER BY to
specify in which order the data should be returned
SELECT i FROM test order by 2*i+i%2;
1
2
3
4
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