在mysql中的表锁，LOCK TABLE t READ;  用读锁锁表，会阻塞其他事务修改表数据
===================================================================
####Session 1
mysql> select * from t;
+------+------+
| id   | name |
+------+------+
|    1 | WW   |
|    2 | SS   |
|    3 | VV   |
+------+------+
3 rows in set (0.00 sec)

####读锁-锁表t
mysql> LOCK TABLE t READ;

####Session 2,可以读取数据
mysql> select * from t where id=1;
+------+------+
| id   | name |
+------+------+
|    1 | WW   |
+------+------+
1 row in set (0.00 sec)

####Session 2, insert数据被阻塞
mysql> insert into t values(4,'LL');

####Session 1, 解除读锁-锁表t
mysql> UNLOCK table;
Query OK, 0 rows affected (0.00 sec)

在mysql中的表锁，LOCK TABLE t WRITE; 用写锁锁表，会阻塞其他事务读和写
===================================================================
####Session 1
mysql> select * from t;
+------+------+
| id   | name |
+------+------+
|    1 | WW   |
|    2 | SS   |
|    3 | VV   |
+------+------+
3 rows in set (0.00 sec)

####Session 1,写锁-锁表t
mysql> LOCK TABLE t WRITE;

####Session 2,读取数据被阻塞
mysql> select * from t where id=1;

####Session 2, insert数据被阻塞
mysql> insert into t values(4,'LL');

####Session 1, 解除读锁-锁表t
mysql> UNLOCK table;
Query OK, 0 rows affected (0.00 sec)
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--待续