Question

我刚刚开始学习SQL，如果您能帮助SELECT查询，将非常感谢。有输入变量：@p_IPN和@p_SecondName，该表具有SECONDNAME，FIRSTNAME，MIDDLENAME和IPN列。

我需要在以下条件下通过指定的输入字符在表中进行搜索：

如果未指定任何变量，则查询应返回整个表；
如果指定了@p_IPN或@p_SecondName，则查询应按IPN LIKE @p_IPN OR SECONDNAME LIKE @p_SecondName执行搜索；
如果同时指定了两个变量，则查询应返回输入字符为@p_IPN和@p_SecondName（IPN LIKE @p_IPN AND SECONDNAME LIKE @p_SecondName）的行

我使用了以下查询：

IF (@p_IPN IS NULL AND @p_SecondName IS NULL)
    SELECT 
        CAST(IPN AS NVARCHAR(MAX)) AS IPN, FIRSTNAME, SECONDNAME, MIDDLENAME 
    FROM
        dbo.BE_BlackList
ELSE IF (@p_IPN IS NULL)
    SELECT 
        CAST(IPN AS NVARCHAR(MAX)) AS IPN, FIRSTNAME, SECONDNAME, MIDDLENAME    
    FROM
        dbo.BE_BlackList
    WHERE 
        SECONDNAME LIKE @p_SecondName
ELSE IF (@p_SecondName IS NULL)
    SELECT 
        CAST(IPN AS NVARCHAR(MAX)) AS IPN, FIRSTNAME, SECONDNAME, MIDDLENAME    
    FROM
        dbo.BE_BlackList
    WHERE 
        IPN LIKE @p_IPN
ELSE
    SELECT 
        CAST(IPN AS NVARCHAR(MAX)) AS IPN, FIRSTNAME, SECONDNAME, MIDDLENAME    
    FROM
        dbo.BE_BlackList
    WHERE 
        IPN LIKE @p_IPN AND SECONDNAME LIKE @p_SecondName

它运作良好，但是，我仍然需要使用SELECT查询获得相同的结果。

我尝试过：

    SELECT CASE WHEN @p_IPN IS NULL AND @p_Secondname IS NULL THEN
            (SELECT cast (IPN AS nvarchar(max)) AS IPN, FIRSTNAME, MIDDLENAME, SECONDNAME FROM dbo.BE_BlackList)

               WHEN @p_SecondName IS NULL THEN
            (SELECT cast(IPN AS nvarchar(max)) AS IPN, FIRSTNAME, MIDDLENAME, SECONDNAME FROM dbo.BE_BlackList
             WHERE IPN LIKE @p_IPN)

               WHEN @p_IPN IS NULL THEN
            (SELECT cast(IPN AS nvarchar(max)) AS IPN, FIRSTNAME, MIDDLENAME, SECONDNAME FROM dbo.BE_BlackList
             WHERE SECONDNAME LIKE @p_Secondname)

         ELSE 
            (SELECT cast (IPN AS nvarchar(max)) AS IPN, FIRSTNAME, MIDDLENAME, SECONDNAME FROM dbo.BE_BlackList
             WHERE SECONDNAME LIKE @p_Secondname AND IPN LIKE @p_IPN)
         END
FROM dbo.BE_BlackList

我收到此错误：

第16层，状态1，第10行，Msg 116
如果未使用EXISTS引入子查询，则只能在选择列表中指定一个表达式。

我不确定如何在这里使用CASE WHEN EXISTS（如果可能的话）。你能帮忙吗？

Answer 1

您可以将WHERE用作条件过滤器，而不是使用IF ELSE

SELECT 
    CAST(IPN AS NVARCHAR(MAX)) AS IPN, FIRSTNAME, SECONDNAME, MIDDLENAME 
FROM
    dbo.BE_BlackList
WHERE 
   (@p_IPN IS NULL OR IPN LIKE @p_IPN)
   AND
   (@p_SecondName IS NULL OR SECONDNAME LIKE @p_SecondName)

Answer 2

问题出在您的CASE WHEN语法上。将CASE WHEN视为一列。换句话说，SELECT CASE WHEN a = b, THEN c FROM dbo.BE_BlackList

您在说SELECT CASE WHEN a = b then SELECT c from dbo.BE_Blacklist-注意，这里有两个选择语句。

协助SQL Server SELECT查询

2 个答案: