The “keys” are fields in the operators:
* Aggregate.groupSet is a bit map, where "group by x, y” would be encoded by
setting bits 2 and 4 if x was the 2nd column (0-based) of the input and y was
the 4th column. Note that “group by y, x” is encoded exactly the same way.
“select distinct” will
By the time the query is translated into relational algebra, SELECT
DISTINCT will have been converted into an Aggregate with no aggregate
functions.
So, for instance,
select distinct deptno from emp
and
select deptno from emp group by deptno
will be indistinguishable if you look at the
