的SQL Server 2012：可以在IIF功能拿起基於條件的最後分配的值

Question

比方說，我有一個表，看起來像這樣：

+---------+-----------+------------+ 
| Company | Quantity |  Date | 
+---------+-----------+------------+ 
| A  |  10000 | 2016-08-01 | 
| B  |  -5000 | 2016-08-01 | 
| C  |  5000 | 2016-08-01 | 
| A  |  5000 | 2016-08-02 | 
| B  |  -2500 | 2016-08-02 | 
| C  |  5000 | 2016-08-02 | 
| A  |   0 | 2016-08-03 | 
| B  |   0 | 2016-08-03 | 
| C  |  5000 | 2016-08-03 | 
+---------+-----------+------------+ 

我試圖創建一個名爲列的視圖IssuerLS如果數量爲+ ve，則列值爲'L'，如果數量爲-ve，列值將爲'S'。這部分很容易與IIF的功能，但我也想用最後已知的值，如果數量爲0，所以我認爲應該是這樣的：

+---------+----------+------------+----------+ 
| Company | Quantity | Date | IssuerLS | 
+---------+----------+------------+----------+ 
| A  | 10000 | 2016-08-01 | L  | 
| B  | -5000 | 2016-08-01 | S  | 
| C  |  5000 | 2016-08-01 | L  | 
| A  |  5000 | 2016-08-02 | L  | 
| B  | -2500 | 2016-08-02 | S  | 
| C  |  5000 | 2016-08-02 | L  | 
| A  |  0 | 2016-08-03 | L  | 
| B  |  0 | 2016-08-03 | S  | 
| C  |  5000 | 2016-08-03 | L  | 
+---------+----------+------------+----------+ 

有沒有辦法做到讓IIF函數來如果數量爲0，則使用每個公司最後一次已知的'L'或'S'值？

謝謝。

Answer 1

;with cte 
    as 
    (select *, 
    case 
    when qty>0 then 'l' 
    when qty<0 then 'S' 
    else null end as newval 
    from #tmp 
    ) 
    select c1.cmp,c1.qty,c1.date, 
    case when newval is null then rplcval else newval end as somecol 
     from cte c1 
    cross apply 
    (
    select top 1 newval as rplcval from cte c2 where c2.date<=c1.date and c1.cmp = c2.cmp 
order by date) b 

Answer 2

可以使用case和outer apply來完成。

SELECT *, 
     CASE WHEN Quantity = 0 THEN CASE WHEN prevQuantity > 0 THEN 'L' ELSE 'S'END 
      ELSE CASE WHEN Quantity > 0 THEN 'L' ELSE 'S' END 
     END 
FROM Table1 t1 
     OUTER APPLY (SELECT TOP 1 
          Quantity prevQuantity 
        FROM Table1 t2 
        WHERE t2.Company = t1.Company 
          AND t2.Date < t1.Date 
          AND t2.Quantity <> 0 
        ORDER BY [Date] DESC 
        ) t2 

，如果你想使用IIF然後

SELECT *, 
     IIF(Quantity <> 0, IIF(Quantity > 0, 'L','S'), IIF(prevQuantity > 0, 'L','S')) 
FROM Table1 t1 
     CROSS APPLY (SELECT TOP 1 
          Quantity prevQuantity 
        FROM Table1 t2 
        WHERE t2.Company = t1.Company 
          AND t2.Date <= t1.Date 
          AND t2.Quantity <> 0 
        ORDER BY [Date] DESC 
        ) t2