mysql索引与视图 原始表student字段： mysql select column_name,data_type - from information_schema.columns - where table_name = 'student';+-------------+-----------+| column_name | data_type |+-------------+-----------+| stu_id | int || stu_n

原始表student字段：

mysql> select column_name,data_type
 -> from information_schema.columns
 -> where table_name = 'student';
+-------------+-----------+
| column_name | data_type |
+-------------+-----------+
| stu_id | int |
| stu_name | varchar |
| stu_tel | int |
| stu_score | int |
+-------------+-----------+
4 rows in set (0.01 sec)

mysql> select * from student;
+--------+----------+---------+-----------+
| stu_id | stu_name | stu_tel | stu_score |
+--------+----------+---------+-----------+
| 1 | a | 151 | 60 |
| 2 | b | 152 | 61 |
| 3 | c | 153 | 62 |
| 4 | d | 154 | 63 |
+--------+----------+---------+-----------+
4 rows in set (0.00 sec)

索引创建格式：

create [  ] index  [ using {btree | hash} ] on table specification (  [, ] )
 := unique | fulltext | spatial
:= [asc | desc]

创建一个最简单的索引：

mysql> create index stu_index 
 -> on student(stu_id);
Query OK, 0 rows affected (0.36 sec)
Records: 0 Duplicates: 0 Warnings: 0

如果没有指定using声明的话，mysql自动创建一个B树。所以上面的索引其实是这样子的：

mysql> create index stu_index using btree 
 -> on student(stu_id asc);
Query OK, 0 rows affected (0.19 sec)
Records: 0 Duplicates: 0 Warnings: 0

也可以为多个列创建唯一的索引：

mysql> create unique index stu_index using hash 
 -> on student(stu_id,stu_name);
Query OK, 0 rows affected (0.19 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> alter table student
 -> add unique index stu_index2
 -> using hash (stu_tel);
Query OK, 0 rows affected (0.36 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> drop index stu_index on student;
Query OK, 0 rows affected (0.22 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> create table student(
 -> stu_id int primary key,
 -> stu_name varchar(5) not null,
 -> stu_tel int(5) unique,
 -> stu_score int(2),
 -> index stu_index(stu_id)
 -> );

只需在表的最后添加创建索引的语句即可。

视图是数据库中的虚拟表，它存储的不是自己的内容，而是经过select从其他表整合而来的。当其他表的内容改变是，视图内的内容跟着改变。在一定条件下，对视图的更新也将改变源表。

创建视图：

create [ or replace ] view  [] as  [with [ cascaded |local ] check option ]
mysql> create view view1 as
 -> (select * from student);
Query OK, 0 rows affected (0.16 sec)
mysql> select * from view1;
+--------+----------+---------+-----------+
| stu_id | stu_name | stu_tel | stu_score |
+--------+----------+---------+-----------+
| 1 | a | 151 | 60 |
| 2 | b | 152 | 61 |
| 3 | c | 153 | 62 |
| 4 | d | 154 | 63 |
+--------+----------+---------+-----------+
4 rows in set (0.00 sec)
创建视图时，如果视图已存在，可用replace重新覆盖创建。
创建视图时还可以更改原始列名。
mysql> create or replace view view1(id,name,tel,score) as
 -> (select * from student);
Query OK, 0 rows affected (0.03 sec)
mysql> select * from view1;
+----+------+------+-------+
| id | name | tel | score |
+----+------+------+-------+
| 1 | a | 151 | 60 |
| 2 | b | 152 | 61 |
| 3 | c | 153 | 62 |
| 4 | d | 154 | 63 |
+----+------+------+-------+
4 rows in set (0.00 sec)
当一个视图可以更新时，就能够使用[with [ cascaded |local ] check option ]选项对更新对有效检查。
删除视图：
drop view view1;

 




下载本文


    
    
显示全文






专题




    

    
动视 51dongshi.net 版权所有
Copyright © 2019-2025