看看MySQL更新数据、删除数据

(1)更新数据
(2)删除数据

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(1)、更新数据

MysqL中使用update语句更新表中的记录，可以更新特定的行或者同事更新所有的行，基本语法如下：

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

【例1】在person表中，更新id值为11的记录，将age字段值改为15，将name字段值改为LimMing，sql语句如下;

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)

• 保证update以where子句结束，通过where子句指定被更新的记录所需要满足的条件，如果忽略where子句，MysqL将更新表中所有的行。

【例2】在person表中，更新age值为19-22的记录，将info字段值都改为student，sql语句如下：

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)

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(2)、删除数据

从数据表删除数据使用delete语句，允许使用where子句指定删除条件。delete语句的基本语法格式如下;

delete from table_name [where < condition>]

• table_name指定要执行删除操作的表。
• where为可选参数，指定删除条件，如果没有，delete语句将删除表中的所有记录。

【例1】在person表中，删除id等于11的记录。

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语句同时删除多条记录，在前面update语句中将age字段值为19-22的记录的info字段值修改为student，在这里删除这些记录，sql语句如下：

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】删除person表中所有记录，sql语句如下：

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)

• 如果想删除表中的所有记录，还可以使用truncate table语句，truncate将直接删除原来的表，并重新创建一个表，其语法格式为truncate table table_name。truncate直接删除表而不是删除记录，因此执行速度比delete快。

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