SQL联接查询

SELECT C.ID D.NAME

FROM dbo.test as c

CROSS JOIN dbo.testt as d;
//把多个表的列放在一起

SELECT E.empid, E.firstname,E.lastname,O.orderid
FROM HR.Employess AS E
   JOIN Sale.orders AS O
    ON E.empid=O.empid;
//两个相同的地方内联接查询

SELECT E.empid, E.firstname,E.lastname,O.orderid
FROM HR.Employess AS E
   JOIN Sale.orders AS O
    ON E.empid=O.empid;
    AND E.ID=O.ID
//多个相同的地方内联接查询

SELECT E.empid, E.firstname,E.lastname,O.orderid
FROM HR.Employess AS E
   JOIN Sale.orders AS O
    ON E.empid<O.empid;
//与内联接相同，而内联接是等值联接，包含等号以外的运算符的联接是不等联接

SELECT  
c.custid,c.companyname,o.orderid,
OD.productid,OD.qty
FROM Sales.customers AS c
 JOIN SALES.Orders as o
 ON c.custid=o.custid
 JOIN Sales.OrderDetails AS OD
 ON o.orderid=OD.orderid;