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drop table if exists t1;
create table t1 (a int, b int not null,unique key (a,b),index(b)) type=myisam;
insert ignore into t1 values (1,1),(2,2),(3,3),(4,4),(5,5),(6,6),(null,7),(9,9),(8,8),(7,7),(null,9),(null,9),(6,6);
explain select * from t1 where a is null;
table type possible_keys key key_len ref rows Extra
t1 ref a a 5 const 3 where used; Using index
explain select * from t1 where a is null and b = 2;
table type possible_keys key key_len ref rows Extra
t1 ref a,b a 9 const,const 1 where used; Using index
explain select * from t1 where a is null and b = 7;
table type possible_keys key key_len ref rows Extra
t1 ref a,b a 9 const,const 1 where used; Using index
explain select * from t1 where a=2 and b = 2;
table type possible_keys key key_len ref rows Extra
t1 const a,b a 9 const,const 1
explain select * from t1 where a<=>b limit 2;
table type possible_keys key key_len ref rows Extra
t1 index NULL a 9 NULL 12 where used; Using index
explain select * from t1 where (a is null or a > 0 and a < 3) and b < 5 limit 3;
table type possible_keys key key_len ref rows Extra
t1 range a,b a 9 NULL 3 where used; Using index
explain select * from t1 where (a is null or a = 7) and b=7;
table type possible_keys key key_len ref rows Extra
t1 ref a,b b 4 const 2 where used
explain select * from t1 where (a is null and b>a) or a is null and b=7 limit 2;
table type possible_keys key key_len ref rows Extra
t1 ref a,b a 5 const 3 where used; Using index
explain select * from t1 where a is null and b=9 or a is null and b=7 limit 3;
table type possible_keys key key_len ref rows Extra
t1 range a,b a 9 NULL 2 where used; Using index
explain select * from t1 where a > 1 and a < 3 limit 1;
table type possible_keys key key_len ref rows Extra
t1 range a a 5 NULL 1 where used; Using index
explain select * from t1 where a > 8 and a < 9;
table type possible_keys key key_len ref rows Extra
t1 range a a 5 NULL 1 where used; Using index
select * from t1 where a is null;
a b
NULL 7
NULL 9
NULL 9
select * from t1 where a is null and b = 7;
a b
NULL 7
select * from t1 where a<=>b limit 2;
a b
1 1
2 2
select * from t1 where (a is null or a > 0 and a < 3) and b < 5 limit 3;
a b
1 1
2 2
select * from t1 where (a is null or a > 0 and a < 3) and b > 7 limit 3;
a b
NULL 9
NULL 9
select * from t1 where (a is null or a = 7) and b=7;
a b
NULL 7
7 7
select * from t1 where a is null and b=9 or a is null and b=7 limit 3;
a b
NULL 7
NULL 9
NULL 9
alter table t1 modify b blob not null, add c int not null, drop key a, add unique key (a,b(20),c), drop key b, add key (b(10));
explain select * from t1 where a is null and b = 2;
table type possible_keys key key_len ref rows Extra
t1 ref a,b a 5 const 3 where used
explain select * from t1 where a is null and b = 2 and c=0;
table type possible_keys key key_len ref rows Extra
t1 ref a,b a 5 const 3 where used
explain select * from t1 where a is null and b = 7 and c=0;
table type possible_keys key key_len ref rows Extra
t1 ref a,b a 5 const 3 where used
explain select * from t1 where a=2 and b = 2;
table type possible_keys key key_len ref rows Extra
t1 ref a,b a 5 const 1 where used
explain select * from t1 where a<=>b limit 2;
table type possible_keys key key_len ref rows Extra
t1 ALL NULL NULL NULL NULL 12 where used
explain select * from t1 where (a is null or a > 0 and a < 3) and b < 5 and c=0 limit 3;
table type possible_keys key key_len ref rows Extra
t1 range a,b a 5 NULL 5 where used
explain select * from t1 where (a is null or a = 7) and b=7 and c=0;
table type possible_keys key key_len ref rows Extra
t1 range a,b a 5 NULL 4 where used
explain select * from t1 where (a is null and b>a) or a is null and b=7 limit 2;
table type possible_keys key key_len ref rows Extra
t1 ref a,b a 5 const 3 where used
explain select * from t1 where a is null and b=9 or a is null and b=7 limit 3;
table type possible_keys key key_len ref rows Extra
t1 ref a,b a 5 const 3 where used
explain select * from t1 where a > 1 and a < 3 limit 1;
table type possible_keys key key_len ref rows Extra
t1 range a a 5 NULL 1 where used
explain select * from t1 where a is null and b=7 or a > 1 and a < 3 limit 1;
table type possible_keys key key_len ref rows Extra
t1 range a,b a 5 NULL 4 where used
explain select * from t1 where a > 8 and a < 9;
table type possible_keys key key_len ref rows Extra
t1 range a a 5 NULL 1 where used
explain select * from t1 where b like "6%";
table type possible_keys key key_len ref rows Extra
t1 range b b 12 NULL 1 where used
select * from t1 where a is null;
a b c
NULL 7 0
NULL 9 0
NULL 9 0
select * from t1 where a is null and b = 7 and c=0;
a b c
NULL 7 0
select * from t1 where a<=>b limit 2;
a b c
1 1 0
2 2 0
select * from t1 where (a is null or a > 0 and a < 3) and b < 5 limit 3;
a b c
1 1 0
2 2 0
select * from t1 where (a is null or a > 0 and a < 3) and b > 7 limit 3;
a b c
NULL 9 0
NULL 9 0
select * from t1 where (a is null or a = 7) and b=7 and c=0;
a b c
NULL 7 0
7 7 0
select * from t1 where a is null and b=9 or a is null and b=7 limit 3;
a b c
NULL 7 0
NULL 9 0
NULL 9 0
select * from t1 where b like "6%";
a b c
6 6 0
drop table t1;
DROP TABLE IF EXISTS t1,t2;
CREATE TABLE t1 (
id int(10) unsigned NOT NULL auto_increment,
uniq_id int(10) unsigned default NULL,
PRIMARY KEY (id),
UNIQUE KEY idx1 (uniq_id)
) TYPE=MyISAM;
CREATE TABLE t2 (
id int(10) unsigned NOT NULL auto_increment,
uniq_id int(10) unsigned default NULL,
PRIMARY KEY (id)
) TYPE=MyISAM;
INSERT INTO t1 VALUES (1,NULL),(2,NULL),(3,1),(4,2),(5,NULL),(6,NULL),(7,3),(8,4),(9,NULL),(10,NULL);
INSERT INTO t2 VALUES (1,NULL),(2,NULL),(3,1),(4,2),(5,NULL),(6,NULL),(7,3),(8,4),(9,NULL),(10,NULL);
explain select id from t1 where uniq_id is null;
table type possible_keys key key_len ref rows Extra
t1 ref idx1 idx1 5 const 1 where used
explain select id from t1 where uniq_id =1;
table type possible_keys key key_len ref rows Extra
t1 const idx1 idx1 5 const 1
UPDATE t1 SET id=id+100 where uniq_id is null;
UPDATE t2 SET id=id+100 where uniq_id is null;
select id from t1 where uniq_id is null;
id
101
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105
106
109
110
select id from t2 where uniq_id is null;
id
101
102
105
106
109
110
DELETE FROM t1 WHERE uniq_id IS NULL;
DELETE FROM t2 WHERE uniq_id IS NULL;
SELECT * FROM t1 ORDER BY uniq_id, id;
id uniq_id
3 1
4 2
7 3
8 4
SELECT * FROM t2 ORDER BY uniq_id, id;
id uniq_id
3 1
4 2
7 3
8 4
DROP table t1,t2;
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