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测试环境：mysql版本
mysql> select @@version;
+-----------+
| @@version |
+-----------+
| 5.6.42 |
+-----------+
1 row in set (0.00 sec)
mysql>
Mysql的事务隔离
-- read-uncommitted ，读未提交
--session 1
mysql> show variables like '%iso%';
+---------------+------------------+
| Variable_name | Value |
+---------------+------------------+
| tx_isolation | READ-UNCOMMITTED |
+---------------+------------------+
1 row in set (0.00 sec)
mysql> select * from t1;
+------+-------+------+
| year | month | day |
+------+-------+------+
| 2000 | 01 | 01 |
| 2000 | 01 | 20 |
| 2000 | 01 | 30 |
| 2000 | 02 | 02 |
| 2000 | 02 | 23 |
| 2000 | 02 | 23 |
| 2018 | 10 | 28 |
| 2018 | 11 | 05 |
| 2018 | 11 | 04 |
| 2018 | 11 | 03 |
| 2018 | 11 | 06 |
| 2018 | 11 | 07 |
+------+-------+------+
12 rows in set (0.00 sec)
mysql> begin;
Query OK, 0 rows affected (0.00 sec)
mysql> insert into t1 values(2018,11,08);
Query OK, 1 row affected (0.00 sec)
mysql> select * from t1;
+------+-------+------+
| year | month | day |
+------+-------+------+
| 2000 | 01 | 01 |
| 2000 | 01 | 20 |
| 2000 | 01 | 30 |
| 2000 | 02 | 02 |
| 2000 | 02 | 23 |
| 2000 | 02 | 23 |
| 2018 | 10 | 28 |
| 2018 | 11 | 05 |
| 2018 | 11 | 04 |
| 2018 | 11 | 03 |
| 2018 | 11 | 06 |
| 2018 | 11 | 07 |
| 2018 | 11 | 08 |
+------+-------+------+
13 rows in set (0.00 sec)
mysql>--session 2
mysql> select * from t1;
+------+-------+------+
| year | month | day |
+------+-------+------+
| 2000 | 01 | 01 |
| 2000 | 01 | 20 |
| 2000 | 01 | 30 |
| 2000 | 02 | 02 |
| 2000 | 02 | 23 |
| 2000 | 02 | 23 |
| 2018 | 10 | 28 |
| 2018 | 11 | 05 |
| 2018 | 11 | 04 |
| 2018 | 11 | 03 |
| 2018 | 11 | 06 |
| 2018 | 11 | 07 |
| 2018 | 11 | 08 |
+------+-------+------+
13 rows in set (0.00 sec)
mysql>
从上面的测试，可以看到，一个事务，并没有commit提交，在其他的会话中，可以看到这个事务。也就是一个事务可以读取其他事务没有提交的数据 。
-- read committed 。类似Oracle的情况
-- session 1 ，插入数据，未提交
mysql> show variables like '%iso%';
+---------------+----------------+
| Variable_name | Value |
+---------------+----------------+
| tx_isolation | READ-COMMITTED |
+---------------+----------------+
1 row in set (0.00 sec)
mysql> select * from t1;
+------+-------+------+
| year | month | day |
+------+-------+------+
| 2000 | 01 | 01 |
| 2000 | 01 | 20 |
| 2000 | 01 | 30 |
| 2000 | 02 | 02 |
| 2000 | 02 | 23 |
| 2000 | 02 | 23 |
| 2018 | 10 | 28 |
| 2018 | 11 | 05 |
| 2018 | 11 | 04 |
| 2018 | 11 | 03 |
| 2018 | 11 | 06 |
| 2018 | 11 | 07 |
+------+-------+------+
12 rows in set (0.00 sec)
mysql> begin;
Query OK, 0 rows affected (0.00 sec)
mysql> insert into t1 values (2018,11,08);
Query OK, 1 row affected (0.00 sec)
mysql>-- session 2上查看 ，没有读取到新插入的数据
mysql> select * from t1;
+------+-------+------+
| year | month | day |
+------+-------+------+
| 2000 | 01 | 01 |
| 2000 | 01 | 20 |
| 2000 | 01 | 30 |
| 2000 | 02 | 02 |
| 2000 | 02 | 23 |
| 2000 | 02 | 23 |
| 2018 | 10 | 28 |
| 2018 | 11 | 05 |
| 2018 | 11 | 04 |
| 2018 | 11 | 03 |
| 2018 | 11 | 06 |
| 2018 | 11 | 07 |
+------+-------+------+
12 rows in set (0.00 sec)
mysql>-- session 1 提交 ，session 2 再次查看，发现看到了提交后的数据
mysql> commit;
Query OK, 0 rows affected (0.02 sec)
mysql>
mysql> select * from t1;
+------+-------+------+
| year | month | day |
+------+-------+------+
| 2000 | 01 | 01 |
| 2000 | 01 | 20 |
| 2000 | 01 | 30 |
| 2000 | 02 | 02 |
| 2000 | 02 | 23 |
| 2000 | 02 | 23 |
| 2018 | 10 | 28 |
| 2018 | 11 | 05 |
| 2018 | 11 | 04 |
| 2018 | 11 | 03 |
| 2018 | 11 | 06 |
| 2018 | 11 | 07 |
| 2018 | 11 | 08 |
+------+-------+------+
13 rows in set (0.00 sec)
mysql>-- 可重复读 ，repeatable-read
-- 是mysql数据库的默认的事务隔离级别。消除了脏读，不可重复读，幻读，很好地保证了事务的一致性。
-- session 1 ，开启一个事务，插入数据，并提交数据。
mysql> show variables like '%iso%';
+---------------+-----------------+
| Variable_name | Value |
+---------------+-----------------+
| tx_isolation | REPEATABLE-READ |
+---------------+-----------------+
1 row in set (0.01 sec)
mysql> begin;
Query OK, 0 rows affected (0.00 sec)
mysql> insert into t1 values (2018,11,09);
Query OK, 1 row affected (0.00 sec)
mysql> commit;
Query OK, 0 rows affected (0.11 sec)
mysql>
mysql> select * from t1;
+------+-------+------+
| year | month | day |
+------+-------+------+
| 2000 | 01 | 01 |
| 2000 | 01 | 20 |
| 2000 | 01 | 30 |
| 2000 | 02 | 02 |
| 2000 | 02 | 23 |
| 2000 | 02 | 23 |
| 2018 | 10 | 28 |
| 2018 | 11 | 05 |
| 2018 | 11 | 04 |
| 2018 | 11 | 03 |
| 2018 | 11 | 06 |
| 2018 | 11 | 07 |
| 2018 | 11 | 08 |
| 2018 | 11 | 09 |
+------+-------+------+
14 rows in set (0.00 sec)
mysql> insert into t1 values (2018,11,10);
Query OK, 1 row affected (0.02 sec)
mysql> commit;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from t1;
+------+-------+------+
| year | month | day |
+------+-------+------+
| 2000 | 01 | 01 |
| 2000 | 01 | 20 |
| 2000 | 01 | 30 |
| 2000 | 02 | 02 |
| 2000 | 02 | 23 |
| 2000 | 02 | 23 |
| 2018 | 10 | 28 |
| 2018 | 11 | 05 |
| 2018 | 11 | 04 |
| 2018 | 11 | 03 |
| 2018 | 11 | 06 |
| 2018 | 11 | 07 |
| 2018 | 11 | 08 |
| 2018 | 11 | 09 |
| 2018 | 11 | 10 |
+------+-------+------+
15 rows in set (0.00 sec)
mysql> commit;
Query OK, 0 rows affected (0.00 sec)
mysql>-- session 2 ，在session 2 的事务中，看不到session1 中提交的数据。如果需要查看到，则在查询语句中增加for update ；
mysql> begin;
Query OK, 0 rows affected (0.00 sec)
mysql>
mysql> select * from t1;
+------+-------+------+
| year | month | day |
+------+-------+------+
| 2000 | 01 | 01 |
| 2000 | 01 | 20 |
| 2000 | 01 | 30 |
| 2000 | 02 | 02 |
| 2000 | 02 | 23 |
| 2000 | 02 | 23 |
| 2018 | 10 | 28 |
| 2018 | 11 | 05 |
| 2018 | 11 | 04 |
| 2018 | 11 | 03 |
| 2018 | 11 | 06 |
| 2018 | 11 | 07 |
| 2018 | 11 | 08 |
| 2018 | 11 | 09 |
+------+-------+------+
14 rows in set (0.00 sec)
-- 增加for update ，可以看到新增加的数据了 。
mysql> mysql> select * from t1 for update;
+------+-------+------+
| year | month | day |
+------+-------+------+
| 2000 | 01 | 01 |
| 2000 | 01 | 20 |
| 2000 | 01 | 30 |
| 2000 | 02 | 02 |
| 2000 | 02 | 23 |
| 2000 | 02 | 23 |
| 2018 | 10 | 28 |
| 2018 | 11 | 05 |
| 2018 | 11 | 04 |
| 2018 | 11 | 03 |
| 2018 | 11 | 06 |
| 2018 | 11 | 07 |
| 2018 | 11 | 08 |
| 2018 | 11 | 09 |
| 2018 | 11 | 10 |
+------+-------+------+
15 rows in set (0.00 sec)
mysql>END