alamb commented on code in PR #15532:
URL: https://github.com/apache/datafusion/pull/15532#discussion_r2029009800
##########
datafusion/optimizer/src/simplify_expressions/expr_simplifier.rs:
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@@ -1447,15 +1449,240 @@ impl<S: SimplifyInfo> TreeNodeRewriter for
Simplifier<'_, S> {
}
}
+ //
+ // Rules for Case of AggregateFunction
+ //
+ //
+
+ // CASE 1:
+
+ // CASE 1-1:
+ // Extraction of Constants in Multiple AGG Calls, currently only
supports SUM
+ //
+ // Before Optimization
+ // SELECT SUM(ResolutionWidth), SUM(ResolutionWidth + 1), ...,
SUM(ResolutionWidth + 89)
+ // FROM hits;
+ //
+ // After Optimization
+ // SELECT SUM(ResolutionWidth),
+ // SUM(ResolutionWidth) + 1 * COUNT(*),
+ // ...,
+ // SUM(ResolutionWidth) + 89 * COUNT(*)
+ // FROM hits;
+ //
+
+ // CASE 1-2
+ // SUM(5 * a + b) => 5 * SUM(a) + SUM(b)
Review Comment:
it is not clear to me this is a better plan -- each `SUM` aggregate has non
trivial overhead (e.g. intermediate results sent between each grouping operator)
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