一、视图

(1)、创建视图

（2）、修改视图

（3）、删除视图

二、索引文件的创建与删除

（1）、创建索引文件

(2)、删除索引文件

ps:使用DROP INDEX语句删除索引。由于索引在逻辑和物理上独立于相关表中的数据，在任何时候删除索引都不会影响表(或其他索引)。如果删除了索弓1.所有SQL程序和应用会继续正常运行，但访问先前有索引的数据会变慢。

三、实战演练

CREATE VIEW V_STU
AS
SELECT *FROM tb_student
GO

CREATE VIEW V_SCO
AS
SELECT * FROM tb_score
GO

CREATE VIEW V_SCORE
AS
SELECT tb_student.sno,sn,DEPT,tb_score.cno,sn,score 
FROM tb_student,tb_course,tb_score
WHERE tb_student.sno=tb_score.sno AND tb_course.cno=tb_score.cno

GO
CREATE VIEW V_NUM_AVG
AS
SELECT DEPT,COUNT(SNO) AS NUM,AVG(YEAR(GETDATE())-YEAR(BIRTHDAY)) AS AVGA 
FROM tb_student GROUP BY dept
GO

CREATE VIEW V_YEAR
AS
SELECT sno,sn,YEAR(BIRTHDAY) AS YEAR
FROM V_STU

GO
CREATE VIEW V_AVG_S_G
AS
SELECT sno,COUNT(score) AS NUM ,AVG(score) AS AVG
FROM V_SCORE
GROUP BY sno
GO

CREATE VIEW V_AVG_C_G
AS
SELECT cno,COUNT(sno) AS NUM,AVG(score) AS AVGE
FROM V_SCORE GROUP BY cno
GO

CREATE VIEW V_YEAR_RJ
AS
SELECT * FROM V_STU WHERE YEAR(birthday)>1986 AND dept='软件工程'
go

CREATE VIEW V_SEX
AS
SELECT * FROM V_STU
WHERE sex='男' AND polity='党员'
GO

ALTER VIEW V_YEAR
AS 
SELECT * FROM V_STU WHERE YEAR(birthday)<1986 AND dept='软件工程'
GO
DROP VIEW V_YEAR

INSERT INTO V_SCO(sno,cno,score) 
VALUES('2020020140','10002',87)

UPDATE V_SCO SET score=90 WHERE sno='2020020140' AND cno='10002'

DELETE FROM V_SCO WHERE sno='2020020140' AND cno='10002'

查询以上所建视图结果

查询方法①

SELECT SNO,SN,AVG(SCORE) FROM  V_SCORE 
WHERE SNO IN (SELECT SNO FROM V_SCORE GROUP BY SNO HAVING AVG(score)>90) GROUP BY sno,sn

查询方法②

SELECT SNO,SN,AVG(SCORE) FROM  V_SCORE 
WHERE sno IN (SELECT SNO FROM V_AVG_S_G WHERE AVG >90)

查询方法①

SELECT SNO,SN,V1.CNO,CN,SCORE FROM V_SCORE V1 ,V_AVG_C_G V2
WHERE V1.cno=V2.cno AND  V1.score>V2.AVGE  --AND V1.cno='C10'

查询方法②

SELECT SNO,SN,V1.CNO,CN,SCORE FROM V_SCORE V1 WHERE score >
(SELECT AVG(score) FROM V_SCORE V2 WHERE V2.cno=V1.cno GROUP BY cno) --AND V1.cno='C10' AND score<85

SELECT dept,COUNT(VS.sno) FROM V_STU VS ,V_AVG_S_G VA
WHERE VS.sno=VA.sno AND VA.AVG>80 GROUP BY VS.dept

CREATE CLUSTERED INDEX IX_SNO ON TB_STUDENT(SNO DESC)

CREATE INDEX IX_CNO ON TB_SCORE(CNO,SCORE DESC)

CREATE UNIQUE INDEX IX_CNO ON TB_COURSE (CNO ASC)

CREATE UNIQUE INDEX IX_SN ON TB_STUDENT(SN)