1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
|
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);
id select_type table type possible_keys key key_len ref rows Extra
1 FIRST 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;
id select_type table type possible_keys key key_len ref rows Extra
1 FIRST t1 ALL x NULL NULL NULL 6
1 FIRST 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 using BTREE (a,b), key using BTREE (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 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
1 2
1 3
1 3
1 4
1 4
1 5
1 5
1 6
1 6
explain select * from tx where a=x order by a,b;
id select_type table type possible_keys key key_len ref rows Extra
x FIRST tx ref a a x const x where used
explain select * from tx where a=x order by b;
id select_type table type possible_keys key key_len ref rows Extra
x FIRST 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;
id select_type table type possible_keys key key_len ref rows Extra
x FIRST tx ref b b x const x where used
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)
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 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%";
id select_type table type possible_keys key key_len ref rows Extra
1 FIRST 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";
id select_type table type possible_keys key key_len ref rows Extra
1 FIRST t1 ref btn btn 10 const 1 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 FIRST 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;
id select_type table type possible_keys key key_len ref rows Extra
1 FIRST 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;
id select_type table type possible_keys key key_len ref rows Extra
1 FIRST 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;
|
