create table t(id int not null primary key,c int default null) engine=innodb;
insert into t(id,c)values(1,1),(2,2),(3,3),(4,4);
session1session2
([email protected]:3306) [test]> show variables like '%iso%';
+---------------+-----------------+
| variable_name | value |
+---------------+-----------------+
| tx_isolation |repeatable-read|
+---------------+-----------------+
([email protected]:3306) [test]> show variables like 'auto%';
+--------------------------+-------+
| variable_name | value |
+--------------------------+-------+
| auto_increment_increment | 1 |
| auto_increment_offset | 1 |
|autocommit|on|
| automatic_sp_privileges | on |
+--------------------------+-------+
([email protected]:3306) [test]> begin;
query ok, 0 rows affected (0.00 sec)
([email protected]:3306) [test]> select * from t;
+----+------+
| id | c |
+----+------+
| 1 | 1 |
| 2 | 2 |
| 3 | 3 |
| 4 | 4 |
+----+------+
4 rows in set (0.00 sec)
session2: ([email protected]:3306) [test]> update t set c=id+1;
([email protected]:3306) [test]> update t set c=0 where id=c;
query ok, 0 rows affected (4.39 sec)
rows matched: 0 changed: 0 warnings: 0
//session1更新失效,update是當前讀,此時已經找不到id=c的值,所以更新失敗
//rc情況,update還是會更新失效,跟隔離級別無關,都是當前讀,只不過rc情況,下面的select就能讀到session2的正確的值
([email protected]:3306) [test]> select * from t;
+----+------+
| id | c |
+----+------+
| 1 | 1 |
| 2 | 2 |
| 3 | 3 |
| 4 | 4 |
+----+------+
4 rows in set (0.00 sec)
([email protected]:3306) [test]> commit;
query ok, 0 rows affected (0.00 sec)
([email protected]:3306) [test]> select * from t;
+----+------+
| id | c |
+----+------+
| 1 | 2 |
| 2 | 3 |
| 3 | 4 |
| 4 | 5 |
+----+------+
4 rows in set (0.00 sec)
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