xuzifu666 commented on code in PR #5003:
URL: https://github.com/apache/calcite/pull/5003#discussion_r3377383637
##########
core/src/main/java/org/apache/calcite/sql/fun/SqlAvgAggFunction.java:
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@@ -86,4 +96,19 @@ public enum Subtype {
VAR_POP,
VAR_SAMP
}
+
+ @Override public @Nullable RexNode getConstantResult(RexBuilder rexBuilder,
+ RelDataType returnType) {
+ // Only statistical functions (variance and standard deviation) return 0
for constant values.
+ // AVG and other functions should not be optimized through this interface.
Review Comment:
Thanks for point out this issue, this requires proper ```NULL``` semantics
handling. When ```GROUP BY``` key/expression is ```NULL```, we generate:
```CASE WHEN ... IS NULL THEN NULL ELSE 0 END``` to preserve correct ```NULL```
semantics.
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