gatesn opened a new pull request, #13736:
URL: https://github.com/apache/datafusion/pull/13736
## Which issue does this PR close?
Fixes #992
## Rationale for this change
Some statistics can propagate through expressions, such as min, max and sum.
In this particular case, I was looking at the ClickBench Q29 and realized we
had no way to report sum statistics to DataFusion (which would also help for
avg).
Q29 looks like this btw:
```sql
SELECT SUM("ResolutionWidth"), SUM("ResolutionWidth" + 1),
SUM("ResolutionWidth" + 2), SUM("ResolutionWidth" + 3), SUM("ResolutionWidth" +
4), ... SUM("ResolutionWidth" + 88), SUM("ResolutionWidth" + 89) FROM hits;
```
## What changes are included in this PR?
`PhysicalExpr` has a new defaulted trait function `compute_statistics` that
takes a `Statistics` and returns statistics for the columnar result of the
expression. (Unlike the linked issue which proposes returning a full Statistics
object).
Further, this PR adds a `sum` statistic to demonstrate the value of
propagation.
## Are these changes tested?
## Are there any user-facing changes?
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