sql;">-- 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 JoinSELECT *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 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(guò)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,StuBirthdayFROM  Student WHERE StuID<=2UNIONSELECT StuID,StuName,StuEnName,StuAge,StuBirthdayFROM dbo.Student WHERE StuID>2--Union 去重復(fù)SELECT StuSexFROM  Student WHERE StuID<=2UNIONSELECT StuSexFROM dbo.Student WHERE StuID>2--Union 顯示全部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