看看MySQL更新數據、刪除數據

(1)更新數據
(2)刪除數據

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(1)、更新數據

MySQL中使用update語句更新表中的記錄，可以更新特定的行或者同事更新所有的行，基本語法如下：

update table_nameset column_name1 = value1,column_name2 = value2,.....,column_namen = valuenwhere (condition);

【例1】在person表中，更新id值為11的記錄，將age字段值改為15，將name字段值改為LimMing，SQL語句如下;

mysql> update person    -> set age =15,name ='LiMing'     -> where id =11;Query OK, 1 row affected (0.05 sec)Rows matched: 1  Changed: 1  Warnings: 0mysql> select * from person where id =11;+----+--------+------+---------+| id | name   | age  | info    |+----+--------+------+---------+| 11 | LiMing |   15 | student |+----+--------+------+---------+1 row in set (0.00 sec)

• 保證update以where子句結束，通過where子句指定被更新的記錄所需要滿足的條件，如果忽略where子句，MySQL將更新表中所有的行。

【例2】在person表中，更新age值為19-22的記錄，將info字段值都改為student，SQL語句如下：

mysql> select * from person where age between 19 and 22;+----+---------+------+------------+| id | name    | age  | info       |+----+---------+------+------------+|  1 | Green   |   21 | Lawyer     ||  2 | Suse    |   22 | dancer     ||  4 | Willam  |   20 | sports man ||  7 | Dale    |   22 | cook       ||  9 | Harry   |   21 | magician   || 10 | Harriet |   19 | pianist    |+----+---------+------+------------+6 rows in set (0.00 sec)mysql> update person  set info='student' where age between 19 and 22;Query OK, 0 rows affected (0.00 sec)Rows matched: 0  Changed: 0  Warnings: 0mysql> select * from person where age between 19 and 22;+----+---------+------+---------+| id | name    | age  | info    |+----+---------+------+---------+|  1 | Green   |   21 | student ||  2 | Suse    |   22 | student ||  4 | Willam  |   20 | student ||  7 | Dale    |   22 | student ||  9 | Harry   |   21 | student || 10 | Harriet |   19 | student |+----+---------+------+---------+6 rows in set (0.00 sec)

(2)、刪除數據

從數據表刪除數據使用delete語句，允許使用where子句指定刪除條件。delete語句的基本語法格式如下;

delete from table_name [where < condition>]

• table_name指定要執行刪除操作的表。
• "where"為可選參數，指定刪除條件，如果沒有，delete語句將刪除表中的所有記錄。

【例1】在person表中，刪除id等于11的記錄。

mysql> select *     -> from person    -> where id =11;+----+--------+------+---------+| id | name   | age  | info    |+----+--------+------+---------+| 11 | LiMing |   15 | student |+----+--------+------+---------+1 row in set (0.00 sec)mysql> delete from person    -> where id = 11;Query OK, 1 row affected (0.05 sec)mysql> select *     -> from person    -> where id = 11;Empty set (0.00 sec)

【例2】在person表中，使用delete語句同時刪除多條記錄，在前面update語句中將age字段值為19-22的記錄的info字段值修改為student，在這里刪除這些記錄，SQL語句如下：

mysql> select * from person where age between 19 and 22;+----+---------+------+---------+| id | name    | age  | info    |+----+---------+------+---------+|  1 | Green   |   21 | student ||  2 | Suse    |   22 | student ||  4 | Willam  |   20 | student ||  7 | Dale    |   22 | student ||  9 | Harry   |   21 | student || 10 | Harriet |   19 | student |+----+---------+------+---------+6 rows in set (0.00 sec)mysql> delete from person where age between 19 and 22;Query OK, 6 rows affected (0.05 sec)mysql> select * from person where age between 19 and 22;Empty set (0.00 sec)

【例3】刪除person表中所有記錄，SQL語句如下：

mysql> select * from person;+----+---------+------+-----------+| id | name    | age  | info      |+----+---------+------+-----------+|  3 | Mary    |   24 | Musician  ||  5 | Laura   |   25 | NULL      ||  6 | Evans   |   27 | secretary ||  8 | Edison  |   28 | singer    || 12 | Beckham |   31 | police    |+----+---------+------+-----------+5 rows in set (0.00 sec)mysql> delete from person;Query OK, 5 rows affected (0.05 sec)mysql> select * from person;Empty set (0.00 sec)

• 如果想刪除表中的所有記錄，還可以使用truncate table語句，truncate將直接刪除原來的表，并重新創建一個表，其語法格式為truncate table table_name。truncate直接刪除表而不是刪除記錄，因此執行速度比delete快。

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