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MDEV-19600: The optimizer should be able to produce rows=1 estimate for unique index with NULLable columns

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Modify best_access_path() to produce rows=1 estimate for null-rejecting
lookups on unique NULL keys.
This commit is contained in:
Sergei Petrunia 2019-05-27 10:40:04 +03:00
commit f7579518e2
11 changed files with 276 additions and 37 deletions
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4
mysql-test/main/invisible_field.result
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@ -404,8 +404,8 @@ b int(11) YES NULL
c int(11) YES NULL
explain select * from t1,t2 where t1.b = t2.c and t1.c = t2.b;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t2 ALL NULL NULL NULL NULL 10
1 SIMPLE t1 ALL b,c NULL NULL NULL 10 Using where; Using join buffer (flat, BNL join)
1 SIMPLE t2 ALL NULL NULL NULL NULL 10 Using where
1 SIMPLE t1 ref b,c b 5 test.t2.c 1 Using where
select * from t1,t2 where t1.b = t2.c and t1.c = t2.b;
a a b c
1 1 1 1