146 lines
3.3 KiB
Markdown
146 lines
3.3 KiB
Markdown
事务保存点
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==========================
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SAVEPOINT 语句可以在事务过程中标记一个"保存点"，事务可以选择回滚到这个点。保存点是可选的，一个事务过程中也可以有多个保存点。
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示例：将一个事务回滚到一个保存点
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-------------------------
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下面示例展示了一个事务中包含多个 DML 语句和多个保存点，然后回滚到其中一个保存点，只丢弃了保存点后面的那部份修改。
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* 查看表当前记录
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```javascript
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obclient> select * from t_insert;
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+----+------+-------+---------------------+
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| id | name | value | gmt_create |
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+----+------+-------+---------------------+
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| 1 | CN | 10001 | 2020-04-03 16:05:45 |
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| 2 | US | 10002 | 2020-04-03 16:05:54 |
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| 3 | UK | 10003 | 2020-04-03 16:05:54 |
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+----+------+-------+---------------------+
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3 rows in set (0.00 sec)
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```
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* 开启一个事务，设置多个保存点信息。
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```javascript
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obclient> set session autocommit=off;
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Query OK, 0 rows affected (0.00 sec)
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obclient> begin;
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Query OK, 0 rows affected (0.00 sec)
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obclient> insert into t_insert(id, name) values(6,'FR');
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Query OK, 1 row affected (0.00 sec)
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obclient> savepoint fr;
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Query OK, 0 rows affected (0.00 sec)
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obclient> insert into t_insert(id, name) values(7,'RU');
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Query OK, 1 row affected (0.00 sec)
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obclient> savepoint ru;
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Query OK, 0 rows affected (0.00 sec)
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obclient> insert into t_insert(id, name) values(8,'CA');
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Query OK, 1 row affected (0.00 sec)
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obclient> savepoint ca;
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Query OK, 0 rows affected (0.00 sec)
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```
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* 当前会话能看到事务未提交的所有修改。
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```javascript
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obclient> select * from t_insert;
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+----+------+-------+---------------------+
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| id | name | value | gmt_create |
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+----+------+-------+---------------------+
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| 1 | CN | 10001 | 2020-04-03 16:05:45 |
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| 2 | US | 10002 | 2020-04-03 16:05:54 |
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| 3 | UK | 10003 | 2020-04-03 16:05:54 |
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| 6 | FR | NULL | 2020-04-03 16:26:22 |
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| 7 | RU | NULL | 2020-04-03 16:26:32 |
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| 8 | CA | NULL | 2020-04-03 16:26:42 |
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+----+------+-------+---------------------+
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6 rows in set (0.00 sec)
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```
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* 回滚事务到其中一个保存点。
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```javascript
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obclient> rollback to savepoint ru;
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Query OK, 0 rows affected (0.00 sec)
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obclient> select * from t_insert;
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+----+------+-------+---------------------+
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| id | name | value | gmt_create |
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+----+------+-------+---------------------+
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| 1 | CN | 10001 | 2020-04-03 16:05:45 |
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| 2 | US | 10002 | 2020-04-03 16:05:54 |
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| 3 | UK | 10003 | 2020-04-03 16:05:54 |
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| 6 | FR | NULL | 2020-04-03 16:26:22 |
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| 7 | RU | NULL | 2020-04-03 16:26:32 |
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+----+------+-------+---------------------+
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5 rows in set (0.01 sec)
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```
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* 提交事务，确认表最新修改包含保存点之前的修改。
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```javascript
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obclient> commit;
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Query OK, 0 rows affected (0.00 sec)
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obclient> select * from t_insert;
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+----+------+-------+---------------------+
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| id | name | value | gmt_create |
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+----+------+-------+---------------------+
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| 1 | CN | 10001 | 2020-04-03 16:05:45 |
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| 2 | US | 10002 | 2020-04-03 16:05:54 |
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| 3 | UK | 10003 | 2020-04-03 16:05:54 |
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| 6 | FR | NULL | 2020-04-03 16:26:22 |
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| 7 | RU | NULL | 2020-04-03 16:26:32 |
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+----+------+-------+---------------------+
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5 rows in set (0.00 sec)
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obclient>
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```
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