利用子查询解决复杂sql问题

在实际编写sql的过程中,我们往往会遇到一些比较复杂的sql场景,这个时候,我们

利用自查询可以解决.

问题: 返回在每月最后实际订单日期发生的订单

T-sql代码

--  返回在每月最后实际订单日期发生的订单
--  (Orders placed on last actual order date of the month)

SELECT  OrderID, CustomerID, EmployeeID, OrderDate
FROM  dbo.Orders
WHERE  OrderDate  IN
  ( SELECT   MAX (OrderDate)
    FROM  dbo.Orders
    GROUP   BY   CONVERT ( CHAR ( 6 ), OrderDate,  112 ))
order   by  OrderDate
GO

返回结果:

OrderID     CustomerID EmployeeID  OrderDate
----------- ---------- ----------- -----------------------
10269       WHITC      5           1996-07-31 00:00:00.000
10294       RATTC      4           1996-08-30 00:00:00.000
10317       LONEP      6           1996-09-30 00:00:00.000
10343       LEHMS      4           1996-10-31 00:00:00.000
10368       ERNSH      2           1996-11-29 00:00:00.000
10399       VAFFE      8           1996-12-31 00:00:00.000
10432       SPLIR      3           1997-01-31 00:00:00.000
10460       FOLKO      8           1997-02-28 00:00:00.000
10461       LILAS      1           1997-02-28 00:00:00.000
10490       HILAA      7           1997-03-31 00:00:00.000
10491       FURIB      8           1997-03-31 00:00:00.000
10522       LEHMS      4           1997-04-30 00:00:00.000
10553       WARTH      2           1997-05-30 00:00:00.000
10554       OTTIK      4           1997-05-30 00:00:00.000
10583       WARTH      2           1997-06-30 00:00:00.000
10584       BLONP      4           1997-06-30 00:00:00.000
10616       GREAL      1           1997-07-31 00:00:00.000
10617       GREAL      4           1997-07-31 00:00:00.000
10650       FAMIA      5           1997-08-29 00:00:00.000
10686       PICCO      2           1997-09-30 00:00:00.000
10687       HUNGO      9           1997-09-30 00:00:00.000
10725       FAMIA      4           1997-10-31 00:00:00.000
10758       RICSU      3           1997-11-28 00:00:00.000
10759       ANATR      3           1997-11-28 00:00:00.000
10806       VICTE      3           1997-12-31 00:00:00.000
10807       FRANS      4           1997-12-31 00:00:00.000
10861       WHITC      4           1998-01-30 00:00:00.000
10862       LEHMS      8           1998-01-30 00:00:00.000
10914       QUEEN      6           1998-02-27 00:00:00.000
10915       TORTU      2           1998-02-27 00:00:00.000
10916       RANCH      1           1998-02-27 00:00:00.000
10987       EASTC      8           1998-03-31 00:00:00.000
10988       RATTC      3           1998-03-31 00:00:00.000
10989       QUEDE      2           1998-03-31 00:00:00.000
11060       FRANS      2           1998-04-30 00:00:00.000
11061       GREAL      4           1998-04-30 00:00:00.000
11062       REGGC      4           1998-04-30 00:00:00.000
11063       HUNGO      3           1998-04-30 00:00:00.000
11074       SIMOB      7           1998-05-06 00:00:00.000
11075       RICSU      8           1998-05-06 00:00:00.000
11076       BONAP      4           1998-05-06 00:00:00.000
11077       RATTC      1           1998-05-06 00:00:00.000

(42 row(s) affected)