Julian Hyde created CALCITE-2132:
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Summary: Unify rewrites for aggregate functions and windowed
aggregate functions
Key: CALCITE-2132
URL: https://issues.apache.org/jira/browse/CALCITE-2132
Project: Calcite
Issue Type: Bug
Reporter: Julian Hyde
Assignee: Julian Hyde
Aggregate functions and windowed aggregate functions. For example, in the
following queries {{AVG(y)}} can be expanded to {{SUM(y) / COUNT(y)}} (or
something similar to account for empty inputs) and {{COUNT(z)}} can be changed
to {{COUNT(*)}} (if {{z}} does not allow null values):
{code}
SELECT x, AVG(y), COUNT(z)
FROM t
GROUP BY x;
SELECT AVG(y) OVER w, COUNT(z) OVER w
FROM t
WINDOW w AS (ORDER BY x RANGE 3 PRECEDING)
{code}
But the rewrites are spread across several places:
{{AggregateReduceFunctionsRule}},
{{StandardConvertletTable.AvgVarianceConvertlet}}, {{RexBuilder.addAggCall}},
and (when CALCITE-2126 is implemented) {{RexBuilder.makeOver}}.
One important distinction is whether the aggregate function can receive the
empty set. For aggregate functions (i.e. with {{GROUP BY}}) the set is never
empty (except for {{GROUP BY ()}}); for windowed aggregate functions the set
may be empty (except if the window includes the current row, e.g. {{ROWS
BETWEEN 3 PRECEDING AND 2 FOLLOWING}} or {{ROWS 2 PRECEDING}} or {{RANGE 5
PRECEDING}}). If the set may be empty, many aggregate functions become nullable.
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