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https://issues.apache.org/jira/browse/CALCITE-370?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14203977#comment-14203977
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Julian Hyde commented on CALCITE-370:
-------------------------------------
Started work in
https://github.com/julianhyde/incubator-calcite/tree/calcite-370.
My plan is to generalize the Aggregate class to have a list of grouping sets.
If you use simple {{GROUP BY x, y}} you will get just one grouping set as if
you had written {{GROUP BY GROUPING SETS (x, y)}}. The output row type will
include indicator columns, one for each distinct grouping expression (see the
{{GROUPING}} function,
[https://docs.oracle.com/cd/B19306_01/server.102/b14223/aggreg.htm#i1007434]).
{code}
public class Aggregate extends SingleRel {
public final BitSet groupKey;
public final List<BitSet> groupSets;
public final GroupingType groupingType;
enum GroupingType {
SINGLE, // one grouping set
ROLLUP, // roll up leading edge: (x, y, z), (x, y), (x), ()
CUBE, // the full 2^n grouping sets
OTHER // not one of the above
}
{code}
The row type for {{select k0, k1, sum(c) as a0, sum(d) as a1, sum(e) as a2 from
t group k0, k1}} would be {{(k0, g0, k1, g1, a0, a1, a2)}}. Note the indicator
columns g0, g1. g0 evaluates {{GROUPING(k0)}}, saying whether this row is a
roll up over all g0 values.
Existing rules will have to be changed to only fire if groupingType == SINGLE,
and skip over the indicator columns.
> Support GROUPING SETS in SQL and algebra (AggregateRel)
> -------------------------------------------------------
>
> Key: CALCITE-370
> URL: https://issues.apache.org/jira/browse/CALCITE-370
> Project: Calcite
> Issue Type: Bug
> Reporter: Julian Hyde
> Assignee: Julian Hyde
>
> Support grouping sets in the relational algebra. This feature would add a new
> field, groupKeys, to aggregate rel that has a set of bit maps, each of which
> has a grouping key.
> For example, if 'group by x, y, z' is represented by
> {code}
> AggregateRel(groupSet={0, 1, 2})
> {code}
> then 'group by grouping sets (x, y, z), (y, z), ()' would be represented by
> {code}
> AggregateRel(groupSet={0, 1, 2}, groupSets=[ {0, 1, 2}, {1, 2}, {} ])
> {code}
> A regular group by, or a group by with a singleton grouping set, would have
> groupSets = null.
> If groupSets is present, the returned row type would include an indicator
> column for each grouping key.
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