MySQL中如何更新数据以及删除数据
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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)
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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