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backport from 6.0:

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Bug #40925: Equality propagation takes non indexed attribute

Query execution plans and execution time of queries like

  select a, b, c from t1
    where a > '2008-11-21' and b = a limit 10

depended on the order of equality operator parameters:
"b = a" and "a = b" are not same. 


An equality propagation algorithm has been fixed:
the substitute_for_best_equal_field function should not
substitute a field for an equal field if both fields belong
to the same table.


mysql-test/r/select.result:
  Added test case for bug #40925.
mysql-test/t/select.test:
  Added test case for bug #40925.
sql/item.cc:
  Bug #40925: Equality propagation takes non indexed attribute
  
  An equality propagation algorithm has been fixed:
  the substitute_for_best_equal_field function should not 
  substitute a field for an equal field if both fields belong
  to the same table.
This commit is contained in:
Gleb Shchepa
2009-04-28 05:19:13 +05:00
parent b7a70c8b3d
commit def0470598
3 changed files with 28 additions and 1 deletions
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13
mysql-test/r/select.result
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@ -4388,4 +4388,17 @@ f3 f4 count
1 abc 1
1 def 2
drop table t1, t2, t3;
CREATE TABLE t1 (a INT KEY, b INT);
INSERT INTO t1 VALUES (1,1), (2,2), (3,3), (4,4);
EXPLAIN EXTENDED SELECT a, b FROM t1 WHERE a > 1 AND a = b LIMIT 2;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 range PRIMARY PRIMARY 4 NULL 3 Using where
Warnings:
Note 1003 select `test`.`t1`.`a` AS `a`,`test`.`t1`.`b` AS `b` from `test`.`t1` where ((`test`.`t1`.`b` = `test`.`t1`.`a`) and (`test`.`t1`.`a` > 1)) limit 2
EXPLAIN EXTENDED SELECT a, b FROM t1 WHERE a > 1 AND b = a LIMIT 2;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 range PRIMARY PRIMARY 4 NULL 3 Using where
Warnings:
Note 1003 select `test`.`t1`.`a` AS `a`,`test`.`t1`.`b` AS `b` from `test`.`t1` where ((`test`.`t1`.`a` = `test`.`t1`.`b`) and (`test`.`t1`.`a` > 1)) limit 2
DROP TABLE t1;
End of 5.0 tests