mysql - 在选择中使用变量

Question

我有一个这样的查询

SELECT ID, ... , 
       (SELECT MAX(EndDate) FROM Projects) As NewestDate,
       (CASE
           WHEN (NewestDate > NOW()) THEN 'More Work is coming'  
           ELSE 'Send Vendors to work' 
       END) Message
FROM SOME_TABLE

即我正在尝试在 CASE 中使用 NewestDate 的值。这可能吗？或者这样的事情可能吗？

谢谢

Answer 1

直接否。不过，您可以使用相同的语句两次:

SELECT ID, ... , 
       (SELECT MAX(EndDate) FROM Projects) As NewestDate,
       (CASE
           WHEN ((SELECT MAX(EndDate) FROM Projects) > NOW()) 
           THEN 'More Work is coming'  
           ELSE 'Send Vendors to work' 
       END) Message
FROM SOME_TABLE

如果你想使用已经计算出来的，请使用子查询:

select t.*,
    (
        case 
            when (NewestDate > NOW())
                then 'More Work is coming'
            else 'Send Vendors to work'
            end
        ) Message
from (
    select ID,
        ...,
        (
            select MAX(EndDate)
            from Projects
            ) as NewestDate
    from SOME_TABLE
    ) t;