planner: improve row count estimation for index range containing correlated columns (#9738) #9937
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eurekaka
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eurekaka
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Mar 28, 2019
| " └─Selection_20 0.80 cop eq(t1.a, test.t.a)", | ||
| " └─TableScan_19 1.00 cop table:t, keep order:false", | ||
| " └─TableScan_19 1.25 cop table:t, keep order:false", |
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For reviewers: this row count change is caused by the fact that index on column c exists, so we would not analyze column c, hence estimated NDV of column c would be ndv = float64(ds.statisticTable.Count) * distinctFactor, which is 8, not 10. This behavior is different with master branch, because after #9315, we would analyze column c even if index on column c exists.
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/run-all-tests tidb-test=release-2.1 tikv=release-2.1 pd=release-2.1 |
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/run-unit-test tidb-test=release-2.1 tikv=release-2.1 pd=release-2.1 |
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cherry-pick #9738