[jira] [Created] (CALCITE-2132) Unify rewrites for aggregate functions and windowed aggregate functions

["Julian Hyde (JIRA)" <ji...@apache.org>]

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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