TSQL：条件查询答案

【问题标题】：TSQL : conditional queryTSQL：条件查询
【发布时间】：2016-09-30 23:54:02
【问题描述】：

我试图找到一种方法来获得最新的Inspection_date 中的Occupancy 和最后一个之前的不相等的结果。

在此示例中，只有数字 RoomID 2 将是唯一的结果，因为：Occupancy for OrderID 201 = 'Vacant' 到 Occupancy for OrderID 202 = 'Occupied'。

我有查询的开头，但似乎找不到结束查询的好逻辑。

| RoomID | OrderID | Occupancy | rn |
+--------+---------+-----------+----+
| 01     | 101     | Vacant    | 1  |
| 01     | 102     | Vacant    | 2  |
| 01     | 103     | Occupied  | 3  |
| 01     | 104     | Vacant    | 4  |
| 02     | 201     | Vacant    | 1  |
| 02     | 202     | Occupied  | 2  |
| 02     | 203     | Vacant    | 3  |
| 03     | 301     | Occupied  | 1  |
| 03     | 302     | Occupied  | 2  |
| 03     | 303     | Occupied  | 3  |
| 03     | 304     | Occupied  | 4  |
| 04     | 401     | Occupied  | 1  |
| 04     | 402     | Occupied  | 2  |
| 04     | 403     | Vacant    | 3  |
| 04     | 404     | Occupied  | 4  |


SELECT i.room_number, order_number, Occupancy , row_number() OVER(PARTITION BY room_number ORDER BY Inspection_date DESC) rn 
FROM #inspection_data i

【问题讨论】：

标签： sql sql-server tsql where

【解决方案1】：

在 SQL Server 2012+ 中，你可以使用lag()，所以是这样的：

SELECT i.*
FROM (SELECT i.room_number, order_number, Occupancy ,
             ROW_NUMER() OVER (PARTITION BY room_number ORDER BY Inspection_date DESC) as seqnum,
             LAG(Occupancy) OVER (PARTITION BY room_number ORDER BY Inspection_date) as prev_Occupancy
      FROM #inspection_data i
     ) i
WHERE prev_Occupancy <> Occupancy AND seqnum = 1 ;

【讨论】：