-- 交叉連接產(chǎn)生笛卡爾值 (X*Y)
SELECT *
FROM  Student
    cross Join dbo.ClassInfo 
--另外一種寫法
SELECT *
FROM  Student , ClassInfo 
-- 內(nèi)連接 (Inner 可以省略)
SELECT *
FROM  Student
    JOIN dbo.ClassInfo ON dbo.Student.Class = dbo.ClassInfo.ID;
-- Inner Join
SELECT *
FROM  Student
    INNER JOIN dbo.ClassInfo ON dbo.Student.Class = dbo.ClassInfo.ID;
   -- on 條件，通常是 主外鍵，但是不限于主外鍵
   -- on 條件，允許有多個(gè)，而且可能是針對(duì)某個(gè)表的
SELECT *
FROM  Student
    INNER JOIN dbo.ClassInfo ON dbo.Student.Class = dbo.ClassInfo.ID
    AND dbo.Student.Class IN (1,2) -- 針對(duì)Student表增加查詢條件
-- 不等于 (笛卡爾值減去 相等的值)
SELECT *
FROM  Student
    INNER JOIN dbo.ClassInfo ON dbo.Student.Class > dbo.ClassInfo.ID;
--自連接 從Class表中查詢到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 Join
SELECT *
FROM  Student
    Left JOIN dbo.ClassInfo ON dbo.Student.Class = dbo.ClassInfo.ID;
-- Right Join
SELECT *
FROM  Student
    RIGHT  JOIN dbo.ClassInfo ON dbo.Student.Class = dbo.ClassInfo.ID;
-- 全外連接
SELECT *
FROM  Student
    FULL OUTER JOIN dbo.ClassInfo ON dbo.Student.Class = dbo.ClassInfo.ID;
-- 外連接和內(nèi)連接的區(qū)別是：
-- 內(nèi)連接，on條件不符合的話，會(huì)過濾掉數(shù)據(jù)
-- 外連接，以保留表為主，on條件成立顯示數(shù)據(jù)，否則顯示NULL
--Union 縱向連接
SELECT StuID,StuName,StuEnName,StuAge,StuBirthday
FROM  Student WHERE StuID=2
UNION
SELECT StuID,StuName,StuEnName,StuAge,StuBirthday
FROM dbo.Student WHERE StuID>2
--Union 去重復(fù)
SELECT StuSex
FROM  Student WHERE StuID=2
UNION
SELECT StuSex
FROM dbo.Student WHERE StuID>2
--Union 顯示全部
SELECT StuSex
FROM  Student WHERE StuID=2
UNION ALL
SELECT StuSex
FROM dbo.Student WHERE StuID>2
--Except 差集,排除
SELECT StuID,StuName,StuEnName,StuAge,StuBirthday
FROM  Student
Except
SELECT StuID,StuName,StuEnName,StuAge,StuBirthday
FROM dbo.Student WHERE StuID=2
--Intersect 交集
SELECT StuID,StuName,StuEnName,StuAge,StuBirthday
FROM  Student WHERE StuID>=2
Except
SELECT StuID,StuName,StuEnName,StuAge,StuBirthday
FROM dbo.Student WHERE StuID=3