mysql> create database bbs_user2;
Query OK, 1 row affected (0.00 sec)
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| bbs_user |
| bbs_user2 |
| mysql |
| performance_schema |
| test |
+--------------------+
6 rows in set (0.00 sec)
mysql> use bbs_user2;
Database changed
mysql> create table one(
-> id int unsigned not null auto_increment primary key,
-> username varchar(32)
-> );
Query OK, 0 rows affected (0.01 sec)
mysql> insert into one(username) values('zhangyi');
Query OK, 1 row affected (0.00 sec)
mysql> insert into one(username) values('zhanger');
Query OK, 1 row affected (0.00 sec)
mysql> insert into one(username) values('zhangsan');
Query OK, 1 row affected (0.00 sec)
mysql> insert into one(username) values('zhangsi');
Query OK, 1 row affected (0.00 sec)
mysql> select * from one;
+----+----------+
| id | username |
+----+----------+
| 1 | zhangyi |
| 2 | zhanger |
| 3 | zhangsan |
| 4 | zhangsi |
+----+----------+
4 rows in set (0.00 sec)
mysql> delete from one where id=3;
Query OK, 1 row affected (0.00 sec)
mysql> select * from one;
+----+----------+
| id | username |
+----+----------+
| 1 | zhangyi |
| 2 | zhanger |
| 4 | zhangsi | //当我删除id 3的时候 没有清理空间
+----+----------+
3 rows in set (0.00 sec)
mysql> insert into one (username) values('zhangwu');
Query OK, 1 row affected (0.00 sec)
mysql> select * from one;
+----+----------+
| id | username |
+----+----------+
| 1 | zhangyi | //重新插入id 5的数据 跑到id 3的地方出现
| 2 | zhanger |
| 5 | zhangwu |
| 4 | zhangsi |
+----+----------+
4 rows in set (0.00 sec)
mysql>
<------optimize修改遗留数据------>
mysql> create database bbs_user;
Query OK, 1 row affected (0.00 sec)
mysql> use bbs_user;
Database changed
mysql> create table one (
-> id int unsigned not null auto_increment primary key,
-> username varchar(32)
-> );
Query OK, 0 rows affected (0.01 sec)
mysql> insert into one (username) values('zhang1');
Query OK, 1 row affected (0.01 sec)
mysql> insert into one (username) values('zhang2');
Query OK, 1 row affected (0.00 sec)
mysql> insert into one (username) values('zhang3');
Query OK, 1 row affected (0.00 sec)
mysql> insert into one (username) values('zhang4');
Query OK, 1 row affected (0.00 sec) //插入数据
mysql> select * from one ;
+----+----------+
| id | username |
+----+----------+
| 1 | zhang1 |
| 2 | zhang2 |
| 3 | zhang3 |
| 4 | zhang4 |
+----+----------+
4 rows in set (0.00 sec)
mysql> delete from one where id=3;
Query OK, 1 row affected (0.00 sec)
mysql> optimize table one; //这里用optimize清理删除id 3后的遗留空间
+--------------+----------+----------+----------+
| Table | Op | Msg_type | Msg_text |
+--------------+----------+----------+----------+
| bbs_user.one | optimize | status | OK |
+--------------+----------+----------+----------+
1 row in set (0.02 sec)
mysql> insert into one (username) values('zhang5');
Query OK, 1 row affected (0.00 sec)
mysql> select * from one;
+----+----------+
| id | username | //再次添加zhangwu数据时 id 5数据下面出现
+----+----------+
| 1 | zhang1 |
| 2 | zhang2 |
| 4 | zhang4 |
| 5 | zhang5 |
+----+----------+
4 rows in set (0.00 sec)
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转载自blog.csdn.net/feiyucity/article/details/84672754
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