DonnyZone commented on a change in pull request #1756: [CALCITE-1824] GROUP_ID
returns wrong result
URL: https://github.com/apache/calcite/pull/1756#discussion_r366202853
##########
File path: core/src/main/java/org/apache/calcite/sql2rel/SqlToRelConverter.java
##########
@@ -3039,6 +3040,113 @@ protected final void createAggImpl(
}
}
+ /**
+ * The {@code GROUP_ID()} function is used to distinguish duplicate groups.
+ * However, as Aggregate normalizes group sets (i.e., sorting, redundancy
removal),
+ * this information is lost in RelNode. Therefore, it is impossible to
+ * implement the function in runtime.
+ *
+ * To fill this gap, an aggregation query that contains {@code GROUP_ID()}
function
+ * will generally be rewritten into UNION when converting to RelNode.
+ *
+ * Also see the discussion in JIRA
+ * <a
href="https://issues.apache.org/jira/browse/CALCITE-1824";>[CALCITE-1824]
+ * GROUP_ID returns wrong result</a>.
+ */
+ private RelNode rewriteAggregateWithGroupId(Blackboard bb,
+ AggregatingSelectScope.Resolved r, AggConverter converter) {
+ final List<AggregateCall> aggregateCalls = converter.getAggCalls();
+ final ImmutableBitSet groupSet = r.groupSet;
+ final Map<ImmutableBitSet, Integer> groupSetCount = r.groupSetCount;
+
+ final List<String> fieldNamesIfNoRewrite = createAggregate(bb, groupSet,
+ r.groupSets, aggregateCalls).getRowType().getFieldNames();
+
+ // For every GROUP_ID value, collect its group sets in map
+ // E.g., GROUPING SETS (a, a, b, c, c, c, c), the map will be
+ // {0 -> (a, b, c), 1 -> (a, c), 2 -> (c), 3 -> (c)},
Review comment:
They are duplicate group set before transformation into to canonical form
`grouping sets (a, b, c)`. The `UnionAll`'s children and corresponding
`group_id` is:
```
Union All
grouping sets(a, b, c) --- 0
grouping sets(a, c) --- 1
grouping sets(c) --- 2
grouping sets(c) --- 3
```
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