如何纠正这个SQL语句？

Question

服务台：

汽车_id	服务日期
101	2016-02-05
102	2017-02-06
103	2017-05-07
104	2017-02-08
105	2017-05-09
106	2016-03-10
101	2016-08-10
101	2016-02-20
106	2016-08-15
106	2016-12-20

预期结果：

汽车_id	服务_日期（最后）	服务_日期（上一个）
101	2016-08-10	2016-02-20
102	2017-02-06	-
103	2017-05-07	-
104	2017-02-08	-
105	2017-05-09	-
106	2016-12-20	2016-08-15
107	-	-
108	-	-

我当前的代码：

WITH B AS
(
    SELECT 
        A.Car_id, A.Service_Date AS Last, 
        LAG(A.Service_Date) OVER (ORDER BY A.Service_Date) AS Previous
    FROM 
        Service AS A
)
SELECT 
    E.Car_id, F.Last, F.Previous
FROM 
    ((SELECT C.Car_id, C.Last, C.Previous
      FROM 
          (SELECT
               B.Car_id, B.Last, B.Previous, 
               ROW_NUMBER() OVER (PARTITION BY B.Car_id ORDER BY B.Last DESC) AS k
           FROM 
               B) AS C
      WHERE C.K = 1)) AS F 
RIGHT JOIN 
    Car AS E ON F.Car_id = E.Car_id  

我目前的输出：

汽车_id	服务_日期（最后）	服务_日期（上一个）
101	2016-08-10	2016-03-10
102	2017-02-06	2016-12-20
103	2017-05-07	2017-02-08
104	2017-02-08	2017-02-06
105	2017-05-09	2017-05-07
106	2016-12-20	2016-08-15
107	空	空
108	空	空

右连接用于从我临时删除的其他表中提取一些列。该代码的问题在于前一个日期列中的某些值似乎不正确。如果没有其他服务日期，则之前的日期列应包含“-”

Car_ID

。

Car_ID = 107

和

108

尚未收到任何服务，因此它们位于服务表中。我认为需要使用

CASE

语句，但我似乎不知道将其放置在哪里。

Answer 1

需要车旁隔断。一旦我们这样做了，我们就可以将其降低到一层嵌套：

WITH windowed As 
(
    SELECT Car_ID, Service_Date
        , LAG(Service_Date) OVER (PARTITION BY Car_ID ORDER BY Service_Date) Prev
        , ROW_NUMBER() OVER (PARTITION BY Car_ID ORDER BY Service_Date DESC) rn
    FROM Service
)
SELECT c.Car_ID, Service_Date As [Service_Date(Last)], Prev As [Service_Date(Previous)]
FROM Car c
LEFT JOIN Windowed w ON w.Car_ID = c.Car_ID AND w.rn = 1
ORDER BY c.Car_ID

在这里查看它的工作原理（感谢巴特开始小提琴）：

https://dbfiddle.uk/ymWlnkjy