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drop table if exists t1;
create table t1 (a int not null,b int not null, primary key using BTREE (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 A NULL NULL NULL BTREE
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 BTREE (c,a);
drop table t1;
create table t1 (a int not null,b int not null, primary key using BTREE (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 using BTREE (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 using BTREE (a);
select * from t1 where a > 736494;
a
802616
869751
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);
table type possible_keys key key_len ref rows Extra
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 using BTREE (x), unique y using BTREE (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 1
1 3
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;
table type possible_keys key key_len ref rows Extra
t1 ALL x NULL NULL NULL 6
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;
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CREATE TABLE t1 ( a int not null default 0, b int not null default 0, key using BTREE (a,b), key using BTREE (b) ) TYPE=HEAP;
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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 1
1 2
1 3
1 4
1 5
1 6
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 1
1 1
1 2
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1 2
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1 3
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1 3
1 4
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1 4
1 5
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1 5
1 6
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1 6
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explain select * from tx where a=x order by a,b;
table type possible_keys key key_len ref rows Extra
tx ref a a x const x where used
explain select * from tx where a=x order by b;
table type possible_keys key key_len ref rows Extra
tx ref a a x const x where used
select * from t1 where b=1;
a b
1 1
1 1
explain select * from tx where b=x;
table type possible_keys key key_len ref rows Extra
tx ref b b x const x where used
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drop table t1;
create table t1 (id int unsigned not null, primary key using BTREE (id)) type=HEAP;
insert into t1 values(1);
select max(id) from t1;
max(id)
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1
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insert into t1 values(2);
select max(id) from t1;
max(id)
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2
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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 using BTREE (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%";
table type possible_keys key key_len ref rows Extra
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 using BTREE (btn,new_col), drop key btn;
update t1 set new_col=btn;
explain select * from t1 where btn="a";
table type possible_keys key key_len ref rows Extra
t1 ref btn btn 10 const 1 where used
explain select * from t1 where btn="a" and new_col="a";
table type possible_keys key key_len ref rows Extra
t1 ref btn btn 11 const,const 1 where used
drop table t1;
CREATE TABLE t1 (
a int default NULL,
b int default NULL,
KEY a using BTREE (a),
UNIQUE b using BTREE (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;
table type possible_keys key key_len ref rows Extra
t1 ref a a 5 const 1 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;
table type possible_keys key key_len ref rows Extra
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 using BTREE (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;
