drop table if exists t1; create table t1 (a int not null,b int not null, primary key (a)) type=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 NULL 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 (c,a); drop table t1; create table t1 (a int not null,b int not null, primary key (a)) type=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 (a)) type=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, type=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) type=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(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 type=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 where used; Using index drop table t1; create table t1 (x int not null, y int not null, key x (x), unique y (y)) type=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 t1.x 1 drop table t1; create table t1 (a int) type=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(a), key(b) ) TYPE=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 (id)) type=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) type=heap; drop table t1; create table t1 (n int) type=heap; drop table if exists t1; CREATE table t1(f1 int not null,f2 char(20) not null,index(f2)) type=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(btn)) type=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 where used select * from t1 where btn like "q%"; btn alter table t1 add column new_col char(1) not null, add key (btn,new_col), drop key btn; update t1 set new_col=btn; 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 14 where used 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 10 where used drop table t1; CREATE TABLE t1 ( a int default NULL, b int default NULL, KEY a (a), UNIQUE b (b) ) type=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 10 where used 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 where used SELECT * FROM t1 WHERE b<=>NULL; a b 99 NULL INSERT INTO t1 VALUES (1,3); Duplicate entry '3' for key 1 DROP TABLE t1; CREATE TABLE t1 (a int not null, primary key(a)) type=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;