MYSQL 事物隔离级别

1，默认隔离级别

mysql> SHOW VARIABLES  LIKE "%ISO%";
+-----------------------+-----------------+
| Variable_name         | Value           |
+-----------------------+-----------------+
| transaction_isolation | REPEATABLE-READ |
| tx_isolation          | REPEATABLE-READ |
+-----------------------+-----------------+
2 rows in set (0.00 sec)

2，初始化测试数据

CREATE TABLE `t` (
  `id` int(11) NOT NULL,
  `c` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB;
insert into t(id, c) values(1,1),(2,2),(3,3),(4,4);

3，事物现象，更新失败？

mysql> begin;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from t;
+----+------+
| id | c    |
+----+------+
|  1 |    1 |
|  2 |    2 |
|  3 |    3 |
|  4 |    4 |
+----+------+
4 rows in set (0.00 sec)

mysql> update t set c=0 where id=c;
Query OK, 0 rows affected (0.00 sec)
Rows matched: 0  Changed: 0  Warnings: 0

mysql> select * from t;
+----+------+
| id | c    |
+----+------+
|  1 |    1 |
|  2 |    2 |
|  3 |    3 |
|  4 |    4 |
+----+------+
4 rows in set (0.01 sec)

4，构造该现象，默认RR隔离级别下，在事物1开启一个事物，在事物2执行更新，并提交，就出现这个现象.