使用 CASE 语句的多个条件

Question

我需要查询一些数据。这是我构建的查询，但对我来说效果不佳。在本示例中，我使用 AdventureWorks 数据库。

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

这对我不起作用。如何在同一 CASE 的 THEN 中拥有多个 where 条件子句？我怎样才能做到这一点？

Answer 1

这不是剪切和粘贴。 CASE 表达式必须返回一个值，而您返回的是一个包含 SQL 的字符串（从技术上讲，它是一个值，但类型错误）。这就是你想写的，我想：

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

我也怀疑这可能在某些方言中不起作用，但现在无法测试（Oracle，我正在看着你），因为没有布尔值。

但是，由于 @url 不依赖于表值，为什么不进行三个不同的查询，并根据您的参数选择要评估的查询呢？

Answer 2

另一种基于amadan的方式：

    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