Details
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Bug
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Status: Closed (View Workflow)
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Major
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Resolution: Fixed
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10.0, 10.1
Description
DROP TABLE IF EXISTS t1;
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CREATE TABLE t1 (a VARCHAR(20));
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INSERT INTO t1 VALUES ('a'),('b');
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EXPLAIN EXTENDED SELECT * FROM t1 WHERE COALESCE(a)='a' AND COALESCE(a)>='a';
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SHOW WARNINGS;
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returns
+-------+------+----------------------------------------------------------------------------------------+
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| Level | Code | Message |
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+-------+------+----------------------------------------------------------------------------------------+
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| Note | 1003 | select `test`.`t1`.`a` AS `a` from `test`.`t1` where (coalesce(`test`.`t1`.`a`) = 'a') |
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+-------+------+----------------------------------------------------------------------------------------+
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I.e. the right AND part with COALESCE() was optimized away from the condition by equal expression propagation.
If I do the same for DATE data type:
DROP TABLE IF EXISTS t1;
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CREATE TABLE t1 (a DATE);
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INSERT INTO t1 VALUES ('2001-01-01'),('2001-01-02');
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EXPLAIN EXTENDED SELECT * FROM t1 WHERE COALESCE(a)=DATE'2001-01-01' AND COALESCE(a)>=DATE'2001-01-01';
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SHOW WARNINGS;
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it returns:
+-------+------+-----------------------------------------------------------------------------------------------------------------------------------------------------------+
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| Level | Code | Message |
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+-------+------+-----------------------------------------------------------------------------------------------------------------------------------------------------------+
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| Note | 1003 | select `test`.`t1`.`a` AS `a` from `test`.`t1` where ((coalesce(`test`.`t1`.`a`) = DATE'2001-01-01') and (coalesce(`test`.`t1`.`a`) >= DATE'2001-01-01')) |
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+-------+------+-----------------------------------------------------------------------------------------------------------------------------------------------------------+
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i.e. equal expression propagation was not applied.