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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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30
mysql-test/main/join.test
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@ -1254,3 +1254,33 @@ SELECT STRAIGHT_JOIN * FROM t1, t2 AS t2_1, t2 AS t2_2
WHERE t2_2.c = t2_1.c AND t2_2.b = t2_1.b AND ( a IS NULL OR t2_1.c = a );
DROP TABLE t1,t2;
--echo #
--echo # MDEV-19600: The optimizer should be able to produce rows=1 estimate for unique index with NULLable columns
--echo #
create table t0(a int);
insert into t0 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
create table t1 (
pk int not null primary key auto_increment,
a int,
b int,
unique key(a)
);
# 10K of null values
insert into t1 (a,b) select null, 12345 from t0 A, t0 B, t0 C;
insert into t1 (a,b) select a,a from t0;
--echo # Simulate InnoDB's persistent statistics (It always uses nulls_equal)
set @tmp1= @@myisam_stats_method;
set myisam_stats_method=nulls_equal;
analyze table t1;
set myisam_stats_method=@tmp1;
show keys from t1;
--echo # t1 must use ref(t1.a=t0.a) and rows must be 1 (and not 45):
explain select * from t0,t1 where t0.a=t1.a;
drop table t0,t1;