18 lines
763 B
Plaintext
18 lines
763 B
Plaintext
CREATE TABLE `access_path_selection` (
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`a` int,
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`b` int,
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KEY `IDX_a` (`a`),
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KEY `IDX_b` (`b`),
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KEY `IDX_ab` (`a`, `b`)
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);
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explain select a from access_path_selection where a < 3;
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# In this query, IDX_ab is better than IDX_a.
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# The reason is that we have to do double scan if we use IDX_a since it doesn't contain column b.
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explain select a, b from access_path_selection where a < 3;
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# In this query, IDX_ab can't be used, so IDX_b is the best.
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explain select a, b from access_path_selection where b < 3;
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explain select a, b from access_path_selection where a < 3 and b < 3;
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# _tidb_rowid should also be considered as PK.
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explain select a, b from access_path_selection where a > 10 order by _tidb_rowid;
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explain select max(_tidb_rowid) from access_path_selection;
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