MySql--视图

MySql总结之视图部分，MySql可以利用复杂查询来进行多表查询，其实它还提供了一种非常方便的方法，那就是视图，可以从单个数据表中筛选部分数据，也可以从多个数据表中筛选数据，然后整合。

/*************************视图************************************************/	
功能类似于多表查询，可以将一个或多个表中的数据挑选出来独立成表

一、创建视图
	1、单源表视图的创建
		mysql> select * from studentInfo;
		+----+--------+-------+-----------+-----------+
		| id | name   | score | subject   | teacher   |
		+----+--------+-------+-----------+-----------+
		|  1 | 小明   | 87.00 | 数学      | 王老师    |
		|  2 | 小红   | 82.00 | 数学      | 王老师    |
		|  3 | 小张   | 83.00 | 数学      | 王老师    |
		|  4 | 小韩   | 88.00 | 数学      | 王老师    |
		|  5 | 小胡   | 88.00 | 计算机    | 张老师    |
		|  6 | 小胡   | 88.00 | 数据库    | 张老师    |
		+----+--------+-------+-----------+-----------+
		6 rows in set (0.00 sec)
	
		mysql> create view hjf.view_score 
			-> AS(SELECT SI.id, SI.name, SI.score, SI.subject, SI.teacher 
			-> from studentInfo SI 
			-> where SI.score >= 85);
		Query OK, 0 rows affected (0.00 sec)

		mysql> select * from view_score;
		+----+--------+-------+-----------+-----------+
		| id | name   | score | subject   | teacher   |
		+----+--------+-------+-----------+-----------+
		|  1 | 小明   | 87.00 | 数学      | 王老师    |
		|  4 | 小韩   | 88.00 | 数学      | 王老师    |
		|  5 | 小胡   | 88.00 | 计算机    | 张老师    |
		|  6 | 小胡   | 88.00 | 数据库    | 张老师    |
		+----+--------+-------+-----------+-----------+
		4 rows in set (0.00 sec)

	2、多源表视图的创建
	mysql> create view hjf.view_test 
		-> AS(select newInfo.id, newInfo.name, newInfo.score, subjectInfo.subjectname, teacherInfo.teachername
		-> from newInfo, subjectInfo, teacherInfo
		-> where newInfo.subjectid = subjectInfo.id and newInfo.teacherid = teacherInfo.id);
	Query OK, 0 rows affected (0.00 sec)

	mysql> select * from view_test;
	+----+--------+-------+-------------+-------------+
	| id | name   | score | subjectname | teachername |
	+----+--------+-------+-------------+-------------+
	|  1 | 小明   | 78.00 | 数学        | 张老师      |
	|  2 | 小红   | 87.00 | 英语        | 王老师      |
	|  3 | 小李   | 67.00 | 语文        | 吴老师      |
	+----+--------+-------+-------------+-------------+
	3 rows in set (0.02 sec)

二、修改视图
	mysql> create or replace view hjf.view_test
		-> AS(select newInfo.id, newInfo.name, newInfo.score, subjectInfo.subjectname
		-> from newInfo, subjectInfo
		-> where newInfo.subjectid = subjectInfo.id);
	Query OK, 0 rows affected (0.01 sec)

	mysql> select * from view_test;
	+----+--------+-------+-------------+
	| id | name   | score | subjectname |
	+----+--------+-------+-------------+
	|  3 | 小李   | 67.00 | 语文        |
	|  1 | 小明   | 78.00 | 数学        |
	|  2 | 小红   | 87.00 | 英语        |
	+----+--------+-------+-------------+
	3 rows in set (0.00 sec)

三、删除视图
	mysql> drop view view_test;
	Query OK, 0 rows affected (0.00 sec)

四、查看视图
	1、查看视图的字段信息
		mysql> describe(desc) view_test;
		+-------------+--------------+------+-----+---------+-------+
		| Field       | Type         | Null | Key | Default | Extra |
		+-------------+--------------+------+-----+---------+-------+
		| id          | int(11)      | NO   |     | NULL    |       |
		| name        | varchar(20)  | YES  |     | NULL    |       |
		| score       | decimal(4,2) | YES  |     | NULL    |       |
		| subjectname | varchar(30)  | YES  |     | NULL    |       |
		+-------------+--------------+------+-----+---------+-------+
		4 rows in set (0.00 sec)

	2、查看创建视图的语句				\G  格式化显示结果
		mysql> show create view view_test\G;
		*************************** 1. row ***************************
						View: view_test
				 Create View: CREATE ALGORITHM=UNDEFINED DEFINER=`root`@`localhost` SQL SECURITY DEFINER VIEW `view_test` AS (select `newInfo`.`id` AS `id`,`newInfo`.`name` AS `name`,`newInfo`.`score` AS `score`,`subjectInfo`.`subjectname` AS `subjectname` from (`newInfo` join `subjectInfo`) where (`newInfo`.`subjectid` = `subjectInfo`.`id`))
		character_set_client: utf8
		collation_connection: utf8_general_ci
		1 row in set (0.00 sec)

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