MySQL刪除命令_DELETE

單表刪除語句：

DELETE [LOW_PRIORITY][IGNORE] FROM tbl_name

    [WHERE where_definition]

    [ORDER BY ...]

    [LIMIT row_count]

 

這里只對delete的常用參數及用法做出介紹。

 

說明：

low_priority：強制delete命令被延遲執行，直到沒有其它客戶端讀取本表時再執行。

ignore：使MySQL忽略delete執行所有的錯誤，而錯誤會以警告的方式返回。

order by...：表中記錄按照指定的順序進行刪除，此子句一般與limit聯用才有意義。

limit：指定刪除操作的指定行范圍。

注意：1）不能把ORDER BY或LIMIT與multiple-table UPDATE（多表更新）同時使用；

           2）當delete伴隨有多個限制條件時，是將多個限制條件執行查詢操作后，再執行對應的刪除操作。

 

（1）簡單單表刪除

語句：delete from table_name where [條件]

示例：

mysql> select * from staff;
+----+----------+-------+
| id | name     | slary |
+----+----------+-------+
|  1 | guoding  |  3200 |
|  2 | dingtao  |  2800 |
|  3 | haofugui | 10000 |
|  4 | guoming  |  3500 |
|  5 | haotian  |  2900 |
|  6 | fengfei  |  3200 |
|  7 | guoting  |  2600 |
|  8 | guoding  |  3200 |
|  9 | xiaohua  |  3200 |
+----+----------+-------+
9 rows in set (0.00 sec)

mysql> delete from staff where id=9; //通過where指定要刪除的記錄或記錄組合
Query OK, 1 row affected (0.00 sec)

mysql> select * from staff;
+----+----------+-------+
| id | name     | slary |
+----+----------+-------+
|  1 | guoding  |  3200 |
|  2 | dingtao  |  2800 |
|  3 | haofugui | 10000 |
|  4 | guoming  |  3500 |
|  5 | haotian  |  2900 |
|  6 | fengfei  |  3200 |
|  7 | guoting  |  2600 |
|  8 | guoding  |  3200 |
+----+----------+-------+
8 rows in set (0.00 sec)

 

（2）刪除-排序、限制

order by...一般與limit搭配使用才有意義。

如：刪除工資最低的記錄

mysql> select * from staff;
+----+----------+-------+
| id | name     | slary |
+----+----------+-------+
|  1 | guoding  |  3200 |
|  2 | dingtao  |  2800 |
|  3 | haofugui | 10000 |
|  4 | guoming  |  3500 |
|  5 | haotian  |  2900 |
|  6 | fengfei  |  3200 |
|  7 | guoting  |  2600 |
|  8 | guoding  |  3200 |
+----+----------+-------+
8 rows in set (0.00 sec)

mysql> delete from staff order by slary asc limit 1; //刪除工資最低的數據記錄
Query OK, 1 row affected (0.00 sec)

mysql> select * from staff;
+----+----------+-------+
| id | name     | slary |
+----+----------+-------+
|  1 | guoding  |  3200 |
|  2 | dingtao  |  2800 |
|  3 | haofugui | 10000 |
|  4 | guoming  |  3500 |
|  5 | haotian  |  2900 |
|  6 | fengfei  |  3200 |
|  8 | guoding  |  3200 |
+----+----------+-------+
7 rows in set (0.00 sec)

 

（3）連接刪除

假設有一個post表與staff對應：

mysql> select * from staff;
+----+----------+-------+
| id | name     | slary |
+----+----------+-------+
|  1 | guoding  |  3200 |
|  2 | dingtao  |  2800 |
|  3 | haofugui | 10000 |
|  4 | guoming  |  3500 |
|  5 | haotian  |  2900 |
|  6 | fengfei  |  3200 |
|  8 | guoding  |  3200 |
+----+----------+-------+
7 rows in set (0.00 sec)

mysql> select * from post;
+-----+----------+-------+
| num | name     | level |
+-----+----------+-------+
|  1 | haotian  | 3     |
|  2 | guoming  | 1     |
|  3 | haofugui | 2     |
+-----+----------+-------+
3 rows in set (0.00 sec)

現在需要從表staff中刪除在post沒有對應記錄的記錄：

mysql> delete staff from staff left join post on staff.name=post.name where post.name is NULL;
Query OK, 4 rows affected (0.00 sec)

mysql> select * from staff;
+----+----------+-------+
| id | name     | slary |
+----+----------+-------+
|  3 | haofugui | 10000 |
|  4 | guoming  |  3500 |
|  5 | haotian  |  2900 |
+----+----------+-------+
3 rows in set (0.00 sec)

在上述刪除命令中，也可以引入別名，方便輸入，如：

mysql> delete A from staff as A left join post as B on A.name=B.name where B.name is NULL;

注意：NULL不可以用等號（B.name=NULL），正確的應該是B.name is NULL