T-SQL ：联接查询练习 (杂)

SELECT E.empid,
  DATEADD(day, D.n - 1, ‘20090612‘) AS dt
FROM HR.Employees AS E
  CROSS JOIN Nums AS D
WHERE D.n <= DATEDIFF(day, ‘20090612‘, ‘20090616‘) + 1
ORDER BY empid, dt;

SELECT C.custid, COUNT(DISTINCT O.orderid) AS numorders, SUM(OD.qty) AS totalqty
FROM Sales.Customers AS C
  JOIN Sales.Orders AS O
    ON O.custid = C.custid
  JOIN Sales.OrderDetails AS OD
    ON OD.orderid = O.orderid
WHERE C.country = N‘USA‘
GROUP BY C.custid;

SELECT C.custid, C.companyname, O.orderid, O.orderdate
FROM Sales.Customers AS C
  LEFT OUTER JOIN Sales.Orders AS O
    ON O.custid = C.custid
    AND O.orderdate = ‘20070212‘;

SELECT DISTINCT C.custid, C.companyname, 
  CASE WHEN O.orderid IS NOT NULL THEN ‘Yes‘ ELSE ‘No‘ END AS [HasOrderOn20070212]
FROM Sales.Customers AS C
  LEFT OUTER JOIN Sales.Orders AS O
    ON O.custid = C.custid
    AND O.orderdate = ‘20070212‘;