replace into和insert into on duplicate key 区别
replace的用法
- 当不冲突时相当于insert，其余列默认值
- 当key冲突时，自增列更新，replace冲突列，其余列默认值
- Com_replace会加1
- Innodb_rows_updated会加1
Insert into …on duplicate key的用法
- 不冲突时相当于insert，其余列默认值
- 当与key冲突时，只update相应字段值。
- Com_insert会加1
- Innodb_rows_inserted会增加1
实验展示
表结构
- create table helei1(
- id int(10) unsigned NOT NULL AUTO_INCREMENT,
- name varchar(20) NOT NULL DEFAULT '',
- age tinyint(3) unsigned NOT NULL default 0,
- PRIMARY KEY(id),
- UNIQUE KEY uk_name (name)
- )
- ENGINE=innodb AUTO_INCREMENT=1
- DEFAULT CHARSET=utf8;
- </br>
表数据
- root@127.0.0.1 (helei)> select * from helei1;
- +----+-----------+-----+
- | id | name | age |
- +----+-----------+-----+
- | 1 | 贺磊 | 26 |
- | 2 | 小明 | 28 |
- | 3 | 小红 | 26 |
- +----+-----------+-----+
- 3 rows in set (0.00 sec)
replace into用法
- root@127.0.0.1 (helei)> replace into helei1 (name) values('贺磊');
- Query OK, 2 rows affected (0.00 sec)
- root@127.0.0.1 (helei)> select * from helei1;
- +----+-----------+-----+
- | id | name | age |
- +----+-----------+-----+
- | 2 | 小明 | 28 |
- | 3 | 小红 | 26 |
- | 4 | 贺磊 | 0 |
- +----+-----------+-----+
- 3 rows in set (0.00 sec)
- root@127.0.0.1 (helei)> replace into helei1 (name) values('爱璇');
- Query OK, 1 row affected (0.00 sec)
- root@127.0.0.1 (helei)> select * from helei1;
- +----+-----------+-----+
- | id | name | age |
- +----+-----------+-----+
- | 2 | 小明 | 28 |
- | 3 | 小红 | 26 |
- | 4 | 贺磊 | 0 |
- | 5 | 爱璇 | 0 |
- +----+-----------+-----+
- 4 rows in set (0.00 sec)
replace的用法
当没有key冲突时，replace into 相当于insert，其余列默认值
当key冲突时，自增列更新，replace冲突列，其余列默认值
Insert into …on duplicate key:
- root@127.0.0.1 (helei)> select * from helei1;
- +----+-----------+-----+
- | id | name | age |
- +----+-----------+-----+
- | 2 | 小明 | 28 |
- | 3 | 小红 | 26 |
- | 4 | 贺磊 | 0 |
- | 5 | 爱璇 | 0 |
- +----+-----------+-----+
- 4 rows in set (0.00 sec)
- root@127.0.0.1 (helei)> insert into helei1 (name,age) values('贺磊',0) on duplicate key update age=100;
- Query OK, 2 rows affected (0.00 sec)
- root@127.0.0.1 (helei)> select * from helei1;
- +----+-----------+-----+
- | id | name | age |
- +----+-----------+-----+
- | 2 | 小明 | 28 |
- | 3 | 小红 | 26 |
- | 4 | 贺磊 | 100 |
- | 5 | 爱璇 | 0 |
- +----+-----------+-----+
- 4 rows in set (0.00 sec)
- root@127.0.0.1 (helei)> select * from helei1;
- +----+-----------+-----+
- | id | name | age |
- +----+-----------+-----+
- | 2 | 小明 | 28 |
- | 3 | 小红 | 26 |
- | 4 | 贺磊 | 100 |
- | 5 | 爱璇 | 0 |
- +----+-----------+-----+
- 4 rows in set (0.00 sec)
- root@127.0.0.1 (helei)> insert into helei1 (name) values('爱璇') on duplicate key update age=120;
- Query OK, 2 rows affected (0.01 sec)
- root@127.0.0.1 (helei)> select * from helei1;
- +----+-----------+-----+
- | id | name | age |
- +----+-----------+-----+
- | 2 | 小明 | 28 |
- | 3 | 小红 | 26 |
- | 4 | 贺磊 | 100 |
- | 5 | 爱璇 | 120 |
- +----+-----------+-----+
- 4 rows in set (0.00 sec)
- root@127.0.0.1 (helei)> insert into helei1 (name) values('不存在') on duplicate key update age=80;
- Query OK, 1 row affected (0.00 sec)
- root@127.0.0.1 (helei)> select * from helei1;
- +----+-----------+-----+
- | id | name | age |
- +----+-----------+-----+
- | 2 | 小明 | 28 |
- | 3 | 小红 | 26 |
- | 4 | 贺磊 | 100 |
- | 5 | 爱璇 | 120 |
- | 8 | 不存在 | 0 |
- +----+-----------+-----+
- 5 rows in set (0.00 sec)
总结
replace into这种用法，相当于如果发现冲突键，先做一个delete操作，再做一个insert 操作，未指定的列使用默认值，这种情况会导致自增主键产生变化，如果表中存在外键或者业务逻辑上依赖主键，那么会出现异常。因此建议使用Insert into …on duplicate key。由于编写时间也很仓促，文中难免会出现一些错误或者不准确的地方，不妥之处恳请读者批评指正。
