JiajunBernoulli commented on PR #3641:
URL: https://github.com/apache/calcite/pull/3641#issuecomment-1933283166
> Another question I have is whether this should be as you wrote it in
RelBuilder, or it should be a rewrite rule in the optimizer. It is a matter of
design choice rather than of correctness.
Thank you for your review.
1. RelBuilder optimization can reuse subexpressions.
- Using RelBuilder
```
LogicalProject(DEPTNO=[$0], CDS=[$1], CS=[$2], SDS=[$3], SS=[$3]) -- SDS is
same as SS
LogicalAggregate(group=[{0}], CDS=[COUNT($1)], CS=[COUNT()], SDS=[SUM($1)])
LogicalAggregate(group=[{0, 1}])
LogicalProject(DEPTNO=[$7], SAL=[$5])
LogicalTableScan(table=[[CATALOG, SALES, EMP]])
```
- Using Rule
```
LogicalProject(DEPTNO=[$0], CDS=[$1], CS=[$2], SDS=[$3], SS=[$4]) -- SDS is
same as SS
LogicalAggregate(group=[{0}], CDS=[COUNT($1)], CS=[COUNT()],
SDS=[SUM($1)], SS=[SUM($1)])
LogicalAggregate(group=[{0, 1}])
LogicalProject(DEPTNO=[$7], SAL=[$5])
LogicalTableScan(table=[[CATALOG, SALES, EMP]])
```
We need other rules to remove same function.
2. RelBuilder is easier to use than Rule.
- RelBuilder: `withRedundantDistinct(flag)` to enable or disable.
- Rule: Add or remove rule in programs.
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