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),(728912); 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 range 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 1 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 22 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 22 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 22 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 22 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 22 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 22 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 22 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 22 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 22 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 44 const,const 6 Using where 1 SIMPLE t1 ref heap_idx heap_idx 22 const 7 Using where drop table t1, t2, t3; create temporary table t1 ( a int, index (a) ) engine=memory; insert into t1 values (1),(2),(3),(4),(5); select a from t1 where a in (1,3); a 1 3 explain select a from t1 where a in (1,3); id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 range a a 5 NULL 2 Using where drop table t1;