其实truncate很容易理解 主要是在多次创表过程中写成truecate 加深一下印象
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| test |
+--------------------+
4 rows in set (0.00 sec)
mysql> create database feiyu;
Query OK, 1 row affected (0.00 sec)
mysql> use feiyu;
Database changed
mysql>
mysql>
mysql>
mysql> create table `one`(
-> id int unsigned not null auto_increment primary key,
-> `username` varchar(50) not null,
-> `password` varchar(32) not null,
-> `age` int not null
-> )engine=myisam default charset=utf8;
Query OK, 0 rows affected (0.00 sec)
mysql> desc one;
+----------+------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+------------------+------+-----+---------+----------------+
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| username | varchar(50) | NO | | NULL | |
| password | varchar(32) | NO | | NULL | |
| age | int(11) | NO | | NULL | |
+----------+------------------+------+-----+---------+----------------+
4 rows in set (0.01 sec)
mysql> insert into one (username,password,age) values('zhang1',123,25),('zhang2'
,123,24);
Query OK, 2 rows affected (0.00 sec)
Records: 2 Duplicates: 0 Warnings: 0
mysql> insert into one (username,password,age) values('zhang3',123,25),('zhang4'
,123,24);
Query OK, 2 rows affected (0.00 sec)
Records: 2 Duplicates: 0 Warnings: 0
mysql> insert into one (username,password,age) values('zhang5',123,25),('zhang6'
,123,24);
Query OK, 2 rows affected (0.00 sec)
Records: 2 Duplicates: 0 Warnings: 0
mysql> select * from one;
+----+----------+----------+-----+
| id | username | password | age |
+----+----------+----------+-----+
| 1 | zhang1 | 123 | 25 |
| 2 | zhang2 | 123 | 24 |
| 3 | zhang3 | 123 | 25 |
| 4 | zhang4 | 123 | 24 |
| 5 | zhang5 | 123 | 25 |
| 6 | zhang6 | 123 | 24 |
+----+----------+----------+-----+
6 rows in set (0.00 sec)
mysql> delete from one order by id desc limit 6;
Query OK, 6 rows affected (0.00 sec) //6条记录全部被删
mysql> insert into one (username,password,age) values('zhang1',123,25),('zhang2'
,123,24);
Query OK, 2 rows affected (0.00 sec)
Records: 2 Duplicates: 0 Warnings: 0
mysql> select * from one;
+----+----------+----------+-----+
| id | username | password | age | //重新插入后 id=7 id=8 也就是说id没有
+----+----------+----------+-----+
| 7 | zhang1 | 123 | 25 | //清空
| 8 | zhang2 | 123 | 24 |
+----+----------+----------+-----+
2 rows in set (0.00 sec)
mysql> truncate one;
Query OK, 0 rows affected (0.00 sec)
mysql> insert into one (username,password,age) values('zhang1',123,25),('zhang2'
,123,24);
Query OK, 2 rows affected (0.00 sec)
Records: 2 Duplicates: 0 Warnings: 0
mysql> select * from one;
+----+----------+----------+-----+
| id | username | password | age |
+----+----------+----------+-----+
| 1 | zhang1 | 123 | 25 | //truncate 会清空所有表数据 id也是从0
| 2 | zhang2 | 123 | 24 | //开始
+----+----------+----------+-----+
2 rows in set (0.00 sec)