Mysql事務隔離級別之讀提交
查看mysql 事務隔離級別
mysql> show variables like '%isolation%';
+---------------+----------------+
| Variable_name | Value |
+---------------+----------------+
| tx_isolation | READ-COMMITTED |
+---------------+----------------+
1 row in set (0.00 sec)
可以看到當前的事務隔離級別爲 READ-COMMITTED 讀提交
下面看看當前隔離級別下的事務隔離詳情，開啓兩個查詢終端A、B。
下面有一個order表，初始數據如下
mysql> select * from `order`;
+----+--------+
| id | number |
+----+--------+
| 13 | 1 |
+----+--------+
1 row in set (0.00 sec)第一步，在A,B中都開啓事務
mysql> start transaction;
Query OK, 0 rows affected (0.00 sec)第二步查詢兩個終端中的number值
- A
mysql> select * from `order`;
+----+--------+
| id | number |
+----+--------+
| 13 | 1 |
+----+--------+
1 row in set (0.00 sec)- B
mysql> select * from `order`;
+----+--------+
| id | number |
+----+--------+
| 13 | 1 |
+----+--------+
1 row in set (0.00 sec)第三步將B中的number修改爲2,但不提交事務
mysql> update `order` set number=2;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0第四步查詢A中的值
mysql> select * from `order`;
+----+--------+
| id | number |
+----+--------+
| 13 | 1 |
+----+--------+
1 row in set (0.00 sec)發現A中的值並沒有修改。
第五步，提交事務B,再次查詢A中的值
- B
mysql> commit;
Query OK, 0 rows affected (0.01 sec)- A
mysql> select * from `order`;
+----+--------+
| id | number |
+----+--------+
| 13 | 2 |
+----+--------+
1 row in set (0.00 sec)發現A中的值已經更改
第六步，提交A中的事務，再次查詢A，B的值。
- A
mysql> commit;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from `order`;
+----+--------+
| id | number |
+----+--------+
| 13 | 2 |
+----+--------+
1 row in set (0.00 sec)- B
mysql> select * from `order`;
+----+--------+
| id | number |
+----+--------+
| 13 | 2 |
+----+--------+
1 row in set (0.00 sec)發現A,B中的值都更改爲2了。
下面給一個簡單的示意圖
