lock tables和unlock tables

1、lock tables table1 read,table2 read,table3 read

[email protected](glc) > show tables;
+---------------+
| Tables_in_glc |
+---------------+
| mobile        |
| user          |
+---------------+
2 rows in set (0.00 sec)

Fri Dec 20 17:42:35 2019
[email protected]-apple-iphone-db00.wh(glc) > show open tables where in_use >=1;
+----------+-------+--------+-------------+
| Database | Table | In_use | Name_locked |
+----------+-------+--------+-------------+
| glc      | user  |      1 |           0 |
+----------+-------+--------+-------------+
1 row in set (0.00 sec)

Fri Dec 20 17:42:47 2019
[email protected]-apple-iphone-db00.wh(glc) > lock tables user read;                          ######### 添加读锁
Query OK, 0 rows affected (0.00 sec)

Fri Dec 20 17:43:03 2019
[email protected]-apple-iphone-db00.wh(glc) > show open tables where in_use >=1;              ########## 表明：添加表读锁后，表被用次数加一
+----------+-------+--------+-------------+
| Database | Table | In_use | Name_locked |
+----------+-------+--------+-------------+
| glc      | user  |      2 |           0 |
+----------+-------+--------+-------------+
1 row in set (0.00 sec)

Fri Dec 20 17:43:08 2019
[email protected]-apple-iphone-db00.wh(glc) > select * from user;                             ########## 表明：可以读取锁住的表的数据。
+------+------+
| id   | name |
+------+------+
|    1 | 1    |
|    2 | 1    |
+------+------+
2 rows in set (0.01 sec)

Fri Dec 20 17:43:37 2019
[email protected]-apple-iphone-db00.wh(glc) > select * from mobile;                            ##########  表明：只能读取锁住的表的数据，不能查看没有锁住的表的数据
ERROR 1100 (HY000): Table ‘mobile‘ was not locked with LOCK TABLES
Fri Dec 20 17:44:11 2019
[email protected]-apple-iphone-db00.wh(glc) >

########################################

在另一个会话线程中执行如下语句：

[email protected](glc) > select * from user;      ################# 表明：一个会话给表添加了读锁，那么不影响其他会话线程读取该表数据
+------+------+
| id   | name |
+------+------+
|    1 | 1    |
|    2 | 1    |
+------+------+
2 rows in set (0.00 sec)

Fri Dec 20 17:54:11 2019
[email protected]-apple-iphone-db00.wh(glc) > insert into user values (3,‘3‘);       ################# 表明：一个会话给表添加了读锁，其他会话线程只能对该表进行读取，而不能对该表执行执行dml和ddl语句。
^CCtrl-C -- sending "KILL QUERY 233531" to server ...
Ctrl-C -- query aborted.
ERROR 1317 (70100): Query execution was interrupted
Fri Dec 20 17:55:59 2019
[email protected]-apple-iphone-db00.wh(glc) > select connection_id();
+-----------------+
| connection_id() |
+-----------------+
|          233531 |
+-----------------+
1 row in set (0.00 sec)

Fri Dec 20 17:57:07 2019
[email protected]-apple-iphone-db00.wh(glc) > show open tables where in_use>0;;
+----------+-------+--------+-------------+
| Database | Table | In_use | Name_locked |
+----------+-------+--------+-------------+
| glc      | user  |      2 |           0 |
+----------+-------+--------+-------------+
1 row in set (0.00 sec)

ERROR:
No query specified

Fri Dec 20 17:57:25 2019
[email protected]-apple-iphone-db00.wh(glc) > lock tables user read;       ################# 表明：多个会话线程可以对同一张表添加读锁。
Query OK, 0 rows affected (0.00 sec)

Fri Dec 20 17:57:57 2019
[email protected]-apple-iphone-db00.wh(glc) >

当一个会话线程执行：

use glc;

lock tables user read;

那么

1）、该会话线程只能查询锁定的这几个表的数据，没有被锁定的表，不能查询到数据

2）、同时阻止其他会话对锁住的表进行事务操作语句和添加write表锁，

3）、其他会话可以对同一个表添加read锁，

4）

执行

原文地址：https://www.cnblogs.com/igoodful/p/12074396.html