CASE語句的多個條件

Question

我需要查詢一些數據。 這是我構建的查詢，但對我來說這不是很好。 對於此示例，我使用的是AdventureWorks數據庫。

SELECT * FROM [Purchasing].[Vendor] WHERE PurchasingWebServiceURL LIKE 
case
// In this case I need all rows to be returned if @url is '' or 'ALL' or NULL
 when (@url IS null OR @url = '' OR @url = 'ALL') then ('''%'' AND PurchasingWebServiceURL IS NULL')
//I need all records which are blank here including nulls
         when (@url = 'blank') then (''''' AND PurchasingWebServiceURL IS NULL' )
//n this condition I need all record which are not like a particular value
         when (@url = 'fail') then ('''%'' AND PurchasingWebServiceURL NOT LIKE ''%treyresearch%''' )
//Else Match the records which are `LIKE` the input value
         else '%' + @url + '%' 
    end

這不適合我。 如何在同一個CASE的THEN中有多個where條件？ 我怎樣才能做到這一點？

Answer 1

這不是剪切和粘貼。 CASE表達式必須返回一個值，並且您將返回一個包含SQL的字符串（從技術上講，它是一個值但類型錯誤的字符串）。 我想這就是你想寫的東西：

SELECT * FROM [Purchasing].[Vendor] WHERE  
CASE
  WHEN @url IS null OR @url = '' OR @url = 'ALL'
    THEN PurchasingWebServiceURL LIKE '%'
  WHEN @url = 'blank'
    THEN PurchasingWebServiceURL = ''
  WHEN @url = 'fail'
    THEN PurchasingWebServiceURL NOT LIKE '%treyresearch%'
  ELSE PurchasingWebServiceURL = '%' + @url + '%' 
END

我也懷疑這可能不適用於某些方言，但現在無法測試（甲骨文，我在看你），因為沒有布爾。

但是，由於@url不依賴於表值，為什么不進行三個不同的查詢，並根據您的參數選擇要評估的查詢？

Answer 2

基於amadan的另一種方式：

    SELECT * FROM [Purchasing].[Vendor] WHERE  

      ( (@url IS null OR @url = '' OR @url = 'ALL') and   PurchasingWebServiceURL LIKE '%')
    or

       ( @url = 'blank' and  PurchasingWebServiceURL = '')
    or
        (@url = 'fail' and  PurchasingWebServiceURL NOT LIKE '%treyresearch%')
    or( (@url not in ('fail','blank','','ALL') and @url is not null and 
          PurchasingWebServiceUrl Like '%'+@ur+'%') 
END