Use exact distinct_count from statistics if exists for COUNT(DISTINCT column)) calculations#20845
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buraksenn wants to merge 4 commits intoapache:mainfrom
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buraksenn
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Mar 10, 2026
| // expressions like casts or literals are not supported. | ||
| let col_expr = expr.as_any().downcast_ref::<expressions::Column>()?; | ||
| if let Precision::Exact(dc) = col_stats[col_expr.index()].distinct_count { | ||
| return Some(ScalarValue::Int64(Some(dc as i64))); |
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This assumes NULL is not counted in distinct_count column. AFAIS from the repository it is not counted so this should be ok but wanted to put a comment here
jonathanc-n
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Mar 10, 2026
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Thanks @buraksenn couple comments
| Ok(()) | ||
| } | ||
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| fn mock_data_with_distinct_count( |
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Are we able to combine these two functions
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I did not exactly understand but changed it to one table driven test
| // expressions like casts or literals are not supported. | ||
| let col_expr = expr.as_any().downcast_ref::<expressions::Column>()?; | ||
| if let Precision::Exact(dc) = col_stats[col_expr.index()].distinct_count { | ||
| return Some(ScalarValue::Int64(Some(dc as i64))); |
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Distinct count is usize, we should deal with the case where it could overflow
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Since other paths were casting as well I did not do it actually but let me do it for all paths
xudong963
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Mar 11, 2026
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Which issue does this PR close?
Does not close but part of #20766
Rationale for this change
If
distinct_countis known for the column from statistics we can directly use it inCOUNT(DISTINCT column))expressions instead of calculating.What changes are included in this PR?
Are these changes tested?
Added additional tests
Are there any user-facing changes?
No