SQL Server中怎么实现多表连接查询功能

SQL Server中怎么实现多表连接查询功能 ，很多新手对此不是很清楚，为了帮助大家解决这个难题，下面小编将为大家详细讲解，有这方面需求的人可以来学习下，希望你能有所收获。

具体代码如下所示：

-- 交叉连接产生笛卡尔值 (X*Y)SELECT *FROM  Student    cross Join dbo.ClassInfo --另外一种写法SELECT *FROM  Student , ClassInfo -- 内连接 (Inner 可以省略)SELECT *FROM  Student    JOIN dbo.ClassInfo ON dbo.Student.Class = dbo.ClassInfo.ID;-- Inner JoinSELECT *FROM  Student    INNER JOIN dbo.ClassInfo ON dbo.Student.Class = dbo.ClassInfo.ID;   -- on 条件，通常是 主外键，但是不限于主外键   -- on 条件，允许有多个，而且可能是针对某个表的SELECT *FROM  Student    INNER JOIN dbo.ClassInfo ON dbo.Student.Class = dbo.ClassInfo.ID    AND dbo.Student.Class IN (1,2) -- 针对Student表增加查询条件-- 不等于 (笛卡尔值减去 相等的值)SELECT *FROM  Student    INNER JOIN dbo.ClassInfo ON dbo.Student.Class <> dbo.ClassInfo.ID;--自连接 从Class表中查询到Class所在的系SELECT T1.* ,T2.ClassName FROM dbo.ClassInfo AS T1    INNER JOIN dbo.ClassInfo AS T2 ON T1.PID=T2.ID-- Left JoinSELECT *FROM  Student    Left JOIN dbo.ClassInfo ON dbo.Student.Class = dbo.ClassInfo.ID;-- Right JoinSELECT *FROM  Student    RIGHT  JOIN dbo.ClassInfo ON dbo.Student.Class = dbo.ClassInfo.ID;-- 全外连接SELECT *FROM  Student    FULL OUTER JOIN dbo.ClassInfo ON dbo.Student.Class = dbo.ClassInfo.ID;-- 外连接和内连接的区别是：-- 内连接，on条件不符合的话，会过滤掉数据-- 外连接，以保留表为主，on条件成立显示数据，否则显示NULL--Union 纵向连接SELECT StuID,StuName,StuEnName,StuAge,StuBirthdayFROM  Student WHERE StuID<=2UNIONSELECT StuID,StuName,StuEnName,StuAge,StuBirthdayFROM dbo.Student WHERE StuID>2--Union 去重复SELECT StuSexFROM  Student WHERE StuID<=2UNIONSELECT StuSexFROM dbo.Student WHERE StuID>2--Union 显示全部SELECT StuSexFROM  Student WHERE StuID<=2UNION ALLSELECT StuSexFROM dbo.Student WHERE StuID>2--Except 差集,排除SELECT StuID,StuName,StuEnName,StuAge,StuBirthdayFROM  StudentExceptSELECT StuID,StuName,StuEnName,StuAge,StuBirthdayFROM dbo.Student WHERE StuID<=2--Intersect 交集SELECT StuID,StuName,StuEnName,StuAge,StuBirthdayFROM  Student WHERE StuID>=2ExceptSELECT StuID,StuName,StuEnName,StuAge,StuBirthdayFROM dbo.Student WHERE StuID<=3

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