Jark Wu created FLINK-7144:
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Summary: Optimize multiple LogicalAggregate into one
Key: FLINK-7144
URL: https://issues.apache.org/jira/browse/FLINK-7144
Project: Flink
Issue Type: Improvement
Components: Table API & SQL
Reporter: Jark Wu
When applying multiple GROUP BY, and no aggregates or expression in the first
GROUP BY, and the second GROUP fields is a subset of first GROUP fields. Then
the first GROUP BY can be removed.
Such as the following SQL ,
{code}
SELECT a FROM (SELECT a,b,c FROM MyTable GROUP BY a, b, c) GROUP BY a
{code}
should be optimized into
{code}
DataStreamGroupAggregate(groupBy=[a], select=[a])
DataStreamCalc(select=[a])
DataStreamScan(table=[[_DataStreamTable_0]])
{code}
but get:
{code}
DataStreamGroupAggregate(groupBy=[a], select=[a])
DataStreamCalc(select=[a])
DataStreamGroupAggregate(groupBy=[a, b, c], select=[a, b, c])
DataStreamScan(table=[[_DataStreamTable_0]])
{code}
I looked for the Calcite built-in rules, but can't find a match one. So maybe
we should implement one , and maybe we should implement it in Calcite.
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