如何为下面给出的查询编写等效的 SQL 案例语句？答案

【问题标题】：How to write the equivalent SQL case statement for query given below?如何为下面给出的查询编写等效的 SQL 案例语句？
【发布时间】：2013-11-13 08:40:47
【问题描述】：

这是我的工作查询：

Query = "select Cust_Id,Card_Number,Clients_Title,Address_Current,Phone_Number,Mobile_Number from Customer_New Where 1=1";
try
{
    if (txt_title.Text != "")
        Query += " and Clients_Title Like '%" + txt_title.Text + "%'";
    if (txt_address.Text != "")
        Query += " and Address_Current Like '%" + txt_address.Text + "%'";
    if (txt_phone.Text != "")
        Query += " and Phone_Number Like '%" + txt_phone.Text + "%'";
    if (txt_mobile.Text != "")
        Query += " and Mobile_Number Like '%" + txt_mobile.Text + "%'";
    if (cbo_location.Text != "")
        Query += " and AreaLocation Like '%" + cbo_location.Text + "%'";
}

catch { }

这里我正在尝试编写其等效的 SQL 案例语句。

SELECT Cust_Id, Clients_Title, Card_Number, Key_Person, Address_Current, Phone_Number, Mobile_Number, AreaLocation
FROM Customer_New
    WHERE  1 = CASE WHEN @Clients_Title != " " THEN  Clients_Title  AND
                              WHEN  @Address_Current != " " THEN  Address_Current  AND
                             WHEN  @Phone_Number != " " THEN  Phone_Number AND
                             WHEN  @Mobile_Number != " " THEN  Mobile_Number AND
                             WHEN  @AreaLocation != " " THEN  AreaLocation 
END

谁能更正我的案例陈述？

【问题讨论】：

看看this question，觉得可能有帮助
CASE 是一个表达式 - 它被评估以产生一个值。它不是一个陈述，也不应该被认为是某种控制流结构。
查看此 case 语句的使用：stackoverflow.com/questions/8730933/…
您应该更新您的问题以包含您在 cmets 中扩展的要求。

标签： sql sqlite

【解决方案1】：

我想你只是想要这个 - 不需要CASE：

SELECT Cust_Id, Clients_Title, Card_Number, Key_Person, Address_Current, Phone_Number, Mobile_Number, AreaLocation
FROM Customer_New
    WHERE
      (@Clients_Title = '' OR Clients_Title LIKE '%'+@Clients_Title+'%') AND
      (@Address_Current = '' OR Address_Current LIKE '%'+@Address_Current+'%') AND
      (@Phone_Number = '' OR Phone_Number LIKE '%'+@Phone_Number+'%') AND
      (@Mobile_Number = '' OR Mobile_Number LIKE '%'+@Mobile_Number+'%') AND
      (@AreaLocation = '' OR AreaLocation LIKE '%'+@AreaLocation+'%')

因为它至少与您的非 SQL 代码非常相似。

【讨论】：

'"' 附近的 WHERE 子句出错。无法解析查询文本。
语法在我刚刚敲好的这个 SQL Fiddle 上看起来不错：sqlfiddle.com/#!5/4e50e/1
仅适用于此：SELECT Cust_Id、Clients_Title、Card_Number、Key_Person、Address_Current、Phone_Number、Mobile_Number、AreaLocation FROM Customer_New .....没有 where 子句有效
我从这个链接看到了case语句的用法：stackoverflow.com/questions/8730933/…
@getche - NULL not 与空字符串相同，这是NULL 似乎第一次出现在你的任何东西中'已经发布了这个问题。如果要将变量与NULL进行比较，则应为@Clients_Title IS NULL OR ...

【解决方案2】：

SELECT        Cust_Id, Clients_Title, Card_Number, Key_Person, Address_Current, Phone_Number, Mobile_Number, AreaLocation
    FROM            Customer_New
        where        (CASE
            WHEN @Clients_Title != ''   THEN Clients_Title=@Clients_Title
          ELSE
             NULL IS NULL
          END)
          AND(CASE
            WHEN @Address_Current != '' THEN Address_Current =@Address_Current
          ELSE
             NULL IS NULL
          END)
                  AND(CASE
            WHEN @Phone_Number != '' THEN Phone_Number=@Phone_Number
          ELSE
             NULL IS NULL
          END)
          AND(CASE
            WHEN @Mobile_Number != '' THEN Mobile_Number=@Mobile_Number
          ELSE
             NULL IS NULL
          END)
          AND(CASE
            WHEN @AreaLocation != '' THEN AreaLocation =@AreaLocation
          ELSE
             NULL IS NULL
          END)

【讨论】：