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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
parent 7060b0320d
commit f7579518e2
11 changed files with 281 additions and 42 deletions
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mysql-test/main/table_elim.result
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@ -279,7 +279,7 @@ insert into t2 values
explain select t1.* from t1 left join t2 on t2.a=t1.a;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index NULL PRIMARY 10 NULL 2 Using index
1 SIMPLE t2 ref a a 3 test.t1.a 2 Using where
1 SIMPLE t2 ref a a 3 test.t1.a 1 Using where
drop table t1, t2;
#
# check UPDATE/DELETE that look like they could be eliminated