Question

我想要实现的是一个查询，它在where子句中有一个动态列名，具体取决于列是否为空。

举个例子，如果一行的约会日期不为空，那么where子句将为：

WHERE `Building ID` = '1' and `Appointment Date`='2013-10-10' ;

如果约会日期为空，则where子句将为：

WHERE `Building ID` = '1' and `Backup Date`='2013-10-10' ;

现在我在where子句中的子查询返回了太多行，因此查询失败了，我应该如何解决这个问题呢？

我的查询如下：

SELECT `Job ID` 
FROM jobs 
WHERE `Building ID` = '1' 
and (select case when `Appointment Date` IS NOT NULL THEN `Appointment Date` 
else `Backup Date` end FROM jobs WHERE `Building ID` = '1') = '2013-10-10'

Answer 1

SELECT `Job ID` 
FROM jobs 
WHERE `Building ID` = '1' 
and case when `Appointment Date` IS NOT NULL 
         then `Appointment Date` = '2013-10-10' 
         else `Backup Date` = '2013-10-10'
    end

Answer 2

使用COALESCE()功能。它返回其第一个非空的参数。

WHERE `Customer ID` = '1' and COALESCE(`Appointment Date`, `Backup Date`) ='2013-10-10' ;

Answer 3

试试这个：

SELECT `Job ID` 
FROM jobs 
WHERE `Building ID` = '1' 
AND ((`Appointment Date` IS NOT NULL AND `Appointment Date` = '2013-10-10') 
      OR
     (`Appointment Date` IS NULL AND `Backup Date` = '2013-10-10'))

Case子查询在where子句中返回太多行

3 个答案: