避免MySQL替換邏輯SQL的坑爹操作
作者：賀磊
本文最主分享一些如何避免MySQL替換邏輯SQL的坑爹操作，關(guān)于replace into和insert into on duplicate key 區(qū)別操作。
replace into和insert into on duplicate key 區(qū)別
replace的用法
- 當(dāng)不沖突時相當(dāng)于insert，其余列默認(rèn)值
- 當(dāng)key沖突時，自增列更新，replace沖突列，其余列默認(rèn)值
- Com_replace會加1
- Innodb_rows_updated會加1
Insert into …on duplicate key的用法
- 不沖突時相當(dāng)于insert，其余列默認(rèn)值
- 當(dāng)與key沖突時，只update相應(yīng)字段值。
- Com_insert會加1
- Innodb_rows_inserted會增加1
實驗展示
表結(jié)構(gòu)
- 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>
表數(shù)據(jù)
- root@127.0.0.1 (helei)> select * from helei1;
- +----+-----------+-----+
- | id | name | age |
- +----+-----------+-----+
- | 1 | 賀磊 | 26 |
- | 2 | 小明 | 28 |
- | 3 | 小紅 | 26 |
- +----+-----------+-----+
- 3 rows in set (0.00 sec)
replace into用法
- root@127.0.0.1 (helei)> replace into helei1 (name) values('賀磊');
- 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 | 小紅 | 26 |
- | 4 | 賀磊 | 0 |
- +----+-----------+-----+
- 3 rows in set (0.00 sec)
- root@127.0.0.1 (helei)> replace into helei1 (name) values('愛璇');
- 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 | 小紅 | 26 |
- | 4 | 賀磊 | 0 |
- | 5 | 愛璇 | 0 |
- +----+-----------+-----+
- 4 rows in set (0.00 sec)
replace的用法
當(dāng)沒有key沖突時，replace into 相當(dāng)于insert，其余列默認(rèn)值
當(dāng)key沖突時，自增列更新，replace沖突列，其余列默認(rèn)值
Insert into …on duplicate key:
- root@127.0.0.1 (helei)> select * from helei1;
- +----+-----------+-----+
- | id | name | age |
- +----+-----------+-----+
- | 2 | 小明 | 28 |
- | 3 | 小紅 | 26 |
- | 4 | 賀磊 | 0 |
- | 5 | 愛璇 | 0 |
- +----+-----------+-----+
- 4 rows in set (0.00 sec)
- root@127.0.0.1 (helei)> insert into helei1 (name,age) values('賀磊',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 | 小紅 | 26 |
- | 4 | 賀磊 | 100 |
- | 5 | 愛璇 | 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 | 小紅 | 26 |
- | 4 | 賀磊 | 100 |
- | 5 | 愛璇 | 0 |
- +----+-----------+-----+
- 4 rows in set (0.00 sec)
- root@127.0.0.1 (helei)> insert into helei1 (name) values('愛璇') 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 | 小紅 | 26 |
- | 4 | 賀磊 | 100 |
- | 5 | 愛璇 | 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 | 小紅 | 26 |
- | 4 | 賀磊 | 100 |
- | 5 | 愛璇 | 120 |
- | 8 | 不存在 | 0 |
- +----+-----------+-----+
- 5 rows in set (0.00 sec)
總結(jié)
replace into這種用法，相當(dāng)于如果發(fā)現(xiàn)沖突鍵，先做一個delete操作，再做一個insert 操作，未指定的列使用默認(rèn)值，這種情況會導(dǎo)致自增主鍵產(chǎn)生變化，如果表中存在外鍵或者業(yè)務(wù)邏輯上依賴主鍵，那么會出現(xiàn)異常。因此建議使用Insert into …on duplicate key。由于編寫時間也很倉促，文中難免會出現(xiàn)一些錯誤或者不準(zhǔn)確的地方，不妥之處懇請讀者批評指正。
責(zé)任編輯：龐桂玉
來源：
51CTO博客
