表结构：

id：自增主键，a：无索引，b：普通索引

CREATE TABLE `test` (

`id` int(11) NOT NULL AUTO_INCREMENT,

`a` int(4) NOT NULL DEFAULT '0',

`b` int(4) NOT NULL DEFAULT '0',

PRIMARY KEY (`id`),

KEY `b` (`b`) USING BTREE

) ENGINE=InnoDB AUTO_INCREMENT=15 DEFAULT CHARSET=utf8;

等值查询加锁

主键索引字段加锁查询

窗口A:

mysql> set autocommit=0;

Query OK, 0 rows affected (0.00 sec)

mysql> select * from test where id = 1 for update;

+----+---+---+

| id | a | b |

+----+---+---+

| 1 | 2 | 1 |

+----+---+---+

1 row in set (0.00 sec)

窗口B:

mysql> update test set a = 11 where id = 1;(被阻塞，等待窗口A中commit后才执行)

mysql> update test set a = 11 where id = 2;(正常执行)

证明根据主键索引字段加锁查询，会锁住该条数据(记录锁)。

普通索引字段加锁查询

窗口A:

mysql> set autocommit=0;

Query OK, 0 rows affected (0.00 sec)

mysql> select * from test where b = 1 for update;

+----+---+---+

| id | a | b |

+----+---+---+

| 1 | 1 | 1 |

| 3 | 3 | 1 |

| 5 | 5 | 1 |

+----+---+---+

3 rows in set (0.00 sec)

窗口B:

mysql> update test set a = 11 where b = 1;(被阻塞，等待窗口A中commit后才执行)

mysql> update test set a = 11 where id = 3;(被阻塞，等待窗口A中commit后才执行)

mysql> insert into test(a,b) value(1,1);(被阻塞，等待窗口A中commit后才执行)

mysql> update test set a = 11 where id = 2;(正常执行)

mysql> insert into test(a,b) value(1,2);(正常执行)

证明根据普通索引字段加锁查询，会锁住符合该条件的所有记录包括不存在的，因此得出锁的是索引，而非数据本身。

无索引字段加锁查询

窗口A:

mysql> set autocommit=0;

Query OK, 0 rows affected (0.00 sec)

mysql> select * from test where a = 1 for update;

+----+---+---+

| id | a | b |

+----+---+---+

| 1 | 1 | 1 |

+----+---+---+

1 row in set (0.00 sec)

窗口B:

mysql> update test set a = 22 where id = 1;(被阻塞，等待窗口A中commit后才执行)

mysql> update test set a = 22 where a = 1;(被阻塞，等待窗口A中commit后才执行)

mysql> update test set a = 22 where b = 1;(被阻塞，等待窗口A中commit后才执行)

mysql> update test set a = 22 where a = 2;(被阻塞，等待窗口A中commit后才执行)

mysql> update test set a = 22 where b = 2;(被阻塞，等待窗口A中commit后才执行)

mysql> update test set a = 22 where id = 2;(被阻塞，等待窗口A中commit后才执行)

mysql> insert into test(a,b) value(22,22);(被阻塞，等待窗口A中commit后才执行)

证明根据无索引字段加锁查询，会锁住整张表，表现形式类似于表锁。

范围查询加锁

窗口A:

mysql> set autocommit=0;

Query OK, 0 rows affected (0.00 sec)

mysql> select * from test where id > 3 and id < 6 for update;

+----+---+---+

| id | a | b |

+----+---+---+

| 5 | 5 | 5 |

+----+---+---+

1 row in set (0.00 sec)

窗口B:

mysql> insert into test(id,a,b) value(4,4,4);(被阻塞，等待窗口A中commit后才执行)

mysql> insert into test(id,a,b) value(6,6,6);(被阻塞，等待窗口A中commit后才执行)

mysql> update test set a = 77 where id = 7;(被阻塞，等待窗口A中commit后才执行)

mysql> update test set a = 33 where id = 3;(正常执行)

mysql> update test set a = 22 where id=8;(正常执行)

证明锁的范围为**(3,7]，既锁住了记录本身(记录锁)，也锁住了索引之间的间隙(间隙锁)，而且把索引后相邻的两个记录也锁住了(临键锁)**。

通过无索引字段范围查询时，同样是锁住整张表。