使用case語句刪除我的SQL查詢中的ISNULL's

Question

declare @sSQL VARCHAR(2000) 

SET sSQL='Select top 20 ID 
FROM Prospects 
WHERE p.StatusID not in (-1,2,4,5,6,7,8,9,12,13,14)' 
+CASE WHEN @state IS NULL THEN '' ELSE CHAR(10) + 'AND P.State = '+ CHAR(39)+@State +CHAR(39) end 

上面的代碼塊不返回任何狀態值，我想維護ISNULL功能。 原來的是有像這樣的where子句 - 'p.State = IsNull（@State，p.State）'

Answer 1

沒有必要在varchar變量中添加查詢。你可以實現它，而無需使用任何變量這樣的 -

解決方案1：

SELECT TOP 20 ID 
FROM Prospects 
WHERE p.StatusID NOT IN (-1,2,4,5,6,7,8,9,12,13,14) 
    AND (
     P.STATE = @State 
     OR @State IS NULL 
     ) 

解決方案2：

SELECT TOP 20 ID 
FROM Prospects 
WHERE p.StatusID NOT IN (-1,2,4,5,6,7,8,9,12,13,14) 
    AND P.STATE = COALESCE(@State, P.STATE) 

解決方案-3：動態查詢（我總是試圖避免）。

SET @sSQL = 'Select top 20 ID 
FROM Prospects 
WHERE p.StatusID not in (-1,2,4,5,6,7,8,9,12,13,14)' + (
     CASE 
      WHEN @state IS NULL 
       THEN '' 
      ELSE ' AND P.State = ' + QUOTENAME(@State, '''') 
      END 
     ) 

Answer 2

嘗試取消特殊字符，只是用空格代替，並把價值@State在單引號：

SET sSQL = 'Select top 20 ID 
FROM Prospects 
WHERE p.StatusID not in (-1,2,4,5,6,7,8,9,12,13,14)' + 
(CASE WHEN @state IS NULL THEN '' ELSE ' AND P.State = ''' + @State + '''' end) 

或者，您可以爲這樣寫：

SET sSQL = 'Select top 20 ID 
FROM Prospects 
WHERE p.StatusID not in (-1,2,4,5,6,7,8,9,12,13,14)' + 
(CASE WHEN @state IS NULL THEN '' ELSE ' AND P.State = @State' end) 

並使用sp_executesql而不是exec來執行語句。