Mysql中表的删除

Mysql中的删除操作

0.准备

创建一张表persons，然后往这张表中导入一些数据：

create table persons(
id int(5) primary key not null,
LastName varchar(20),
FirstName  varchar(20),
Address varchar(20),
City varchar(20));

insert into persons values
(1,'Adams','John','Oxford Street','London'),
(2,'Bush','George','Fifth Avenue','New York'),
(3,'Carter','Thomas','Changan Street','Beijing');

1.delete

• • 
    
• 01.结合where子句可以删除表中某一行
• 02.可以在不删除表的情况下删除所有的行。这意味着表的结构、属性和索引都是完整的：
  • 
    

mysql> select * from persons;
+----+----------+-----------+----------------+----------+
| id | LastName | FirstName | Address        | City     |
+----+----------+-----------+----------------+----------+
|  1 | Adams    | John      | Oxford Street  | London   |
|  2 | Bush     | George    | Fifth Avenue   | New York |
|  3 | Carter   | Thomas    | Changan Street | Beijing  |
+----+----------+-----------+----------------+----------+
3 rows in set (0.02 sec)

mysql> delete from persons;
Query OK, 3 rows affected (0.05 sec)

mysql> select * from persons;
Empty set (0.00 sec)

mysql> desc persons;
+-----------+-------------+------+-----+---------+-------+
| Field     | Type        | Null | Key | Default | Extra |
+-----------+-------------+------+-----+---------+-------+
| id        | int(5)      | NO   | PRI | NULL    |       |
| LastName  | varchar(20) | YES  |     | NULL    |       |
| FirstName | varchar(20) | YES  |     | NULL    |       |
| Address   | varchar(20) | YES  |     | NULL    |       |
| City      | varchar(20) | YES  |     | NULL    |       |
+-----------+-------------+------+-----+---------+-------+
5 rows in set (0.01 sec)

2.drop

• 01.可以轻松删除索引，表和数据库。

• • 
    
• 001.删除索引​​alter table tableName drop index index_name​​
• 002.删除表【表数据和表结构都被删除】
  • 
    

mysql> drop tables persons;
Query OK, 0 rows affected (0.08 sec)

mysql> select * from persons;
ERROR 1146 (42S02): Table 'mydatabase.persons' doesn't exist

mysql> desc persons;
ERROR 1146 (42S02): Table 'mydatabase.persons' doesn't exist

3.truncate[与delete相同]

• 1.仅删除表内的数据，但并不删除表结构

mysql> truncate table persons;
Query OK, 0 rows affected (0.25 sec)

mysql> select * from persons;
Empty set (0.00 sec)

mysql> desc persons;
+-----------+-------------+------+-----+---------+-------+
| Field     | Type        | Null | Key | Default | Extra |
+-----------+-------------+------+-----+---------+-------+
| id        | int(5)      | NO   | PRI | NULL    |       |
| LastName  | varchar(20) | YES  |     | NULL    |       |
| FirstName | varchar(20) | YES  |     | NULL    |       |
| Address   | varchar(20) | YES  |     | NULL    |       |
| City      | varchar(20) | YES  |     | NULL    |       |
+-----------+-------------+------+-----+---------+-------+
5 rows in set (0.01 sec)