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drop table if exists t1,t2;
create table t1 (a int not null,b int not null, primary key using HASH (a)) engine=heap comment="testing heaps" avg_row_length=100 min_rows=1 max_rows=100;
insert into t1 values(1,1),(2,2),(3,3),(4,4);
delete from t1 where a=1 or a=0;
show keys from t1;
Table Non_unique Key_name Seq_in_index Column_name Collation Cardinality Sub_part Packed Null Index_type Comment
t1 0 PRIMARY 1 a NULL 3 NULL NULL HASH
select * from t1;
a b
2 2
3 3
4 4
select * from t1 where a=4;
a b
4 4
update t1 set b=5 where a=4;
update t1 set b=b+1 where a>=3;
replace t1 values (3,3);
select * from t1;
a b
2 2
3 3
4 6
alter table t1 add c int not null, add key using HASH (c,a);
drop table t1;
create table t1 (a int not null,b int not null, primary key using HASH (a)) engine=heap comment="testing heaps";
insert into t1 values(1,1),(2,2),(3,3),(4,4);
delete from t1 where a > 0;
select * from t1;
a b
drop table t1;
create table t1 (a int not null,b int not null, primary key using HASH (a)) engine=heap comment="testing heaps";
insert into t1 values(1,1),(2,2),(3,3),(4,4);
alter table t1 modify a int not null auto_increment, engine=myisam, comment="new myisam table";
select * from t1;
a b
1 1
2 2
3 3
4 4
drop table t1;
create table t1 (a int not null) engine=heap;
insert into t1 values (869751),(736494),(226312),(802616);
select * from t1 where a > 736494;
a
869751
802616
alter table t1 add unique uniq_id using HASH (a);
select * from t1 where a > 736494;
a
869751
802616
select * from t1 where a = 736494;
a
736494
select * from t1 where a=869751 or a=736494;
a
736494
869751
select * from t1 where a in (869751,736494,226312,802616);
a
226312
736494
802616
869751
alter table t1 engine=myisam;
explain select * from t1 where a in (869751,736494,226312,802616);
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index uniq_id uniq_id 4 NULL 4 Using where; Using index
drop table t1;
create table t1 (x int not null, y int not null, key x using HASH (x), unique y using HASH (y))
engine=heap;
insert into t1 values (1,1),(2,2),(1,3),(2,4),(2,5),(2,6);
select * from t1 where x=1;
x y
1 3
1 1
select * from t1,t1 as t2 where t1.x=t2.y;
x y x y
1 1 1 1
2 2 2 2
1 3 1 1
2 4 2 2
2 5 2 2
2 6 2 2
explain select * from t1,t1 as t2 where t1.x=t2.y;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL x NULL NULL NULL 6
1 SIMPLE t2 eq_ref y y 4 test.t1.x 1
drop table t1;
create table t1 (a int) engine=heap;
insert into t1 values(1);
select max(a) from t1;
max(a)
1
drop table t1;
CREATE TABLE t1 ( a int not null default 0, b int not null default 0, key using HASH (a), key using HASH (b) ) ENGINE=HEAP;
insert into t1 values(1,1),(1,2),(2,3),(1,3),(1,4),(1,5),(1,6);
select * from t1 where a=1;
a b
1 6
1 5
1 4
1 3
1 2
1 1
insert into t1 values(1,1),(1,2),(2,3),(1,3),(1,4),(1,5),(1,6);
select * from t1 where a=1;
a b
1 6
1 5
1 4
1 3
1 2
1 1
1 6
1 5
1 4
1 3
1 2
1 1
drop table t1;
create table t1 (id int unsigned not null, primary key using HASH (id)) engine=HEAP;
insert into t1 values(1);
select max(id) from t1;
max(id)
1
insert into t1 values(2);
select max(id) from t1;
max(id)
2
replace into t1 values(1);
drop table t1;
create table t1 (n int) engine=heap;
drop table t1;
create table t1 (n int) engine=heap;
drop table if exists t1;
CREATE table t1(f1 int not null,f2 char(20) not
null,index(f2)) engine=heap;
INSERT into t1 set f1=12,f2="bill";
INSERT into t1 set f1=13,f2="bill";
INSERT into t1 set f1=14,f2="bill";
INSERT into t1 set f1=15,f2="bill";
INSERT into t1 set f1=16,f2="ted";
INSERT into t1 set f1=12,f2="ted";
INSERT into t1 set f1=12,f2="ted";
INSERT into t1 set f1=12,f2="ted";
INSERT into t1 set f1=12,f2="ted";
delete from t1 where f2="bill";
select * from t1;
f1 f2
16 ted
12 ted
12 ted
12 ted
12 ted
drop table t1;
create table t1 (btn char(10) not null, key using HASH (btn)) engine=heap;
insert into t1 values ("hello"),("hello"),("hello"),("hello"),("hello"),("a"),("b"),("c"),("d"),("e"),("f"),("g"),("h"),("i");
explain select * from t1 where btn like "q%";
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL btn NULL NULL NULL 14 Using where
select * from t1 where btn like "q%";
btn
alter table t1 add column new_col char(1) not null, add key using HASH (btn,new_col), drop key btn;
update t1 set new_col=left(btn,1);
explain select * from t1 where btn="a";
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL btn NULL NULL NULL 11 Using where
explain select * from t1 where btn="a" and new_col="a";
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref btn btn 11 const,const 2 Using where
drop table t1;
CREATE TABLE t1 (
a int default NULL,
b int default NULL,
KEY a using HASH (a),
UNIQUE b using HASH (b)
) engine=heap;
INSERT INTO t1 VALUES (NULL,99),(99,NULL),(1,1),(2,2),(1,3);
SELECT * FROM t1 WHERE a=NULL;
a b
explain SELECT * FROM t1 WHERE a IS NULL;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref a a 5 const 1 Using where
SELECT * FROM t1 WHERE a<=>NULL;
a b
NULL 99
SELECT * FROM t1 WHERE b=NULL;
a b
explain SELECT * FROM t1 WHERE b IS NULL;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref b b 5 const 1 Using where
SELECT * FROM t1 WHERE b<=>NULL;
a b
99 NULL
INSERT INTO t1 VALUES (1,3);
ERROR 23000: Duplicate entry '3' for key 1
DROP TABLE t1;
CREATE TABLE t1 (a int not null, primary key using HASH (a)) engine=heap;
INSERT into t1 values (1),(2),(3),(4),(5),(6),(7),(8),(9),(10),(11);
DELETE from t1 where a < 100;
SELECT * from t1;
a
DROP TABLE t1;
create table t1
(
a char(8) not null,
b char(20) not null,
c int not null,
key (a)
) engine=heap;
insert into t1 values ('aaaa', 'prefill-hash=5',0);
insert into t1 values ('aaab', 'prefill-hash=0',0);
insert into t1 values ('aaac', 'prefill-hash=7',0);
insert into t1 values ('aaad', 'prefill-hash=2',0);
insert into t1 values ('aaae', 'prefill-hash=1',0);
insert into t1 values ('aaaf', 'prefill-hash=4',0);
insert into t1 values ('aaag', 'prefill-hash=3',0);
insert into t1 values ('aaah', 'prefill-hash=6',0);
explain select * from t1 where a='aaaa';
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref a a 8 const 1 Using where
explain select * from t1 where a='aaab';
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref a a 8 const 1 Using where
explain select * from t1 where a='aaac';
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref a a 8 const 1 Using where
explain select * from t1 where a='aaad';
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref a a 8 const 1 Using where
insert into t1 select * from t1;
explain select * from t1 where a='aaaa';
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref a a 8 const 1 Using where
explain select * from t1 where a='aaab';
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref a a 8 const 1 Using where
explain select * from t1 where a='aaac';
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref a a 8 const 1 Using where
explain select * from t1 where a='aaad';
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref a a 8 const 1 Using where
flush tables;
explain select * from t1 where a='aaaa';
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref a a 8 const 2 Using where
explain select * from t1 where a='aaab';
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref a a 8 const 2 Using where
explain select * from t1 where a='aaac';
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref a a 8 const 2 Using where
explain select * from t1 where a='aaad';
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref a a 8 const 2 Using where
create table t2 as select * from t1;
delete from t1;
insert into t1 select * from t2;
explain select * from t1 where a='aaaa';
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref a a 8 const 1 Using where
explain select * from t1 where a='aaab';
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref a a 8 const 1 Using where
explain select * from t1 where a='aaac';
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref a a 8 const 1 Using where
explain select * from t1 where a='aaad';
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref a a 8 const 1 Using where
drop table t1, t2;
create table t1 (
id int unsigned not null primary key auto_increment,
name varchar(20) not null,
index heap_idx(name),
index btree_idx using btree(name)
) engine=heap;
create table t2 (
id int unsigned not null primary key auto_increment,
name varchar(20) not null,
index btree_idx using btree(name),
index heap_idx(name)
) engine=heap;
insert into t1 (name) values ('Matt'), ('Lilu'), ('Corbin'), ('Carly'),
('Suzy'), ('Hoppy'), ('Burrito'), ('Mimi'), ('Sherry'), ('Ben'), ('Phil'),
('Emily'), ('Mike');
insert into t2 select * from t1;
explain select * from t1 where name='matt';
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref heap_idx,btree_idx heap_idx 20 const 1 Using where
explain select * from t2 where name='matt';
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t2 ref btree_idx,heap_idx btree_idx 20 const 1 Using where
explain select * from t1 where name='Lilu';
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref heap_idx,btree_idx heap_idx 20 const 1 Using where
explain select * from t2 where name='Lilu';
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t2 ref btree_idx,heap_idx btree_idx 20 const 1 Using where
explain select * from t1 where name='Phil';
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref heap_idx,btree_idx heap_idx 20 const 1 Using where
explain select * from t2 where name='Phil';
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t2 ref btree_idx,heap_idx btree_idx 20 const 1 Using where
explain select * from t1 where name='Lilu';
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref heap_idx,btree_idx heap_idx 20 const 1 Using where
explain select * from t2 where name='Lilu';
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t2 ref btree_idx,heap_idx btree_idx 20 const 1 Using where
insert into t1 (name) select name from t2;
insert into t1 (name) select name from t2;
insert into t1 (name) select name from t2;
insert into t1 (name) select name from t2;
insert into t1 (name) select name from t2;
insert into t1 (name) select name from t2;
flush tables;
select count(*) from t1 where name='Matt';
count(*)
7
explain select * from t1 ignore index (btree_idx) where name='matt';
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref heap_idx heap_idx 20 const 7 Using where
show index from t1;
Table Non_unique Key_name Seq_in_index Column_name Collation Cardinality Sub_part Packed Null Index_type Comment
t1 0 PRIMARY 1 id NULL 91 NULL NULL HASH
t1 1 heap_idx 1 name NULL 13 NULL NULL HASH
t1 1 btree_idx 1 name A NULL NULL NULL BTREE
show index from t1;
Table Non_unique Key_name Seq_in_index Column_name Collation Cardinality Sub_part Packed Null Index_type Comment
t1 0 PRIMARY 1 id NULL 91 NULL NULL HASH
t1 1 heap_idx 1 name NULL 13 NULL NULL HASH
t1 1 btree_idx 1 name A NULL NULL NULL BTREE
create table t3
(
a varchar(20) not null,
b varchar(20) not null,
key (a,b)
) engine=heap;
insert into t3 select name, name from t1;
show index from t3;
Table Non_unique Key_name Seq_in_index Column_name Collation Cardinality Sub_part Packed Null Index_type Comment
t3 1 a 1 a NULL NULL NULL NULL HASH
t3 1 a 2 b NULL 15 NULL NULL HASH
show index from t3;
Table Non_unique Key_name Seq_in_index Column_name Collation Cardinality Sub_part Packed Null Index_type Comment
t3 1 a 1 a NULL NULL NULL NULL HASH
t3 1 a 2 b NULL 15 NULL NULL HASH
explain select * from t1 ignore key(btree_idx), t3 where t1.name='matt' and t3.a = concat('',t1.name) and t3.b=t1.name;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t3 ref a a 40 const,const 6 Using where
1 SIMPLE t1 ref heap_idx heap_idx 20 const 7 Using where
drop table t1, t2, t3;
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