视图 view
1、创建视图
视图本质是SQL指令
基本语法
-- 可以是单表数据,也可以是连接查询,联合查询或子查询
create view 视图名字 as select 指令
示例
mysql> select * from my_student;
+----+--------+----------+------+--------+
| id | name | class_id | age | gender |
+----+--------+----------+------+--------+
| 1 | 刘备 | 1 | 18 | 2 |
| 2 | 李四 | 1 | 19 | 1 |
| 3 | 王五 | NULL | 20 | 2 |
| 4 | 张飞 | NULL | 21 | 1 |
| 5 | 关羽 | NULL | 22 | 2 |
| 6 | 曹操 | 1 | 20 | NULL |
+----+--------+----------+------+--------+
6 rows in set (0.00 sec)
mysql> select * from my_class;
+----+--------+
| id | name |
+----+--------+
| 1 | 一班 |
| 3 | 三班 |
+----+--------+
2 rows in set (0.00 sec)
-- 创建视图
create view student_class_view as
select s.*, c.name class_name from my_student as s
left join my_class as c
on s.class_id = c.id;
查看视图结构,视图本身是虚拟表,所以关于表的操作都适用于视图
show tables;
show create view <table_name>;
desc <table_name>;
2、使用视图
视图是一张虚拟表,可以直接把视图当做表操作,视图本身没有数据,是临时执行select语句得到对应的结果,视图主要用于查询操作
基本语法
select 字段列表 from 视图名字 [子句];
示例
select * from student_class_view;
+----+--------+----------+------+--------+------------+
| id | name | class_id | age | gender | class_name |
+----+--------+----------+------+--------+------------+
| 1 | 刘备 | 1 | 18 | 2 | 一班 |
| 2 | 李四 | 1 | 19 | 1 | 一班 |
| 3 | 王五 | NULL | 20 | 2 | NULL |
| 4 | 张飞 | NULL | 21 | 1 | NULL |
| 5 | 关羽 | NULL | 22 | 2 | NULL |
| 6 | 曹操 | 1 | 20 | NULL | 一班 |
+----+--------+----------+------+--------+------------+
6 rows in set (0.00 sec)
3、修改视图
本质是修改视图对应的查语句
基本语法
alter view 视图名字 as select 语句;
示例
alter view student_class_view as
select s.id, s.name, c.name class_name from my_student as s
left join my_class as c
on s.class_id = c.id;
mysql> select * from student_class_view;
+----+--------+------------+
| id | name | class_name |
+----+--------+------------+
| 1 | 刘备 | 一班 |
| 2 | 李四 | 一班 |
| 3 | 王五 | NULL |
| 4 | 张飞 | NULL |
| 5 | 关羽 | NULL |
| 6 | 曹操 | 一班 |
+----+--------+------------+
4、删除视图
基本语法
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drop view 视图名字;
示例
drop view student_class_view;