Question

我有以下sql：

SELECT id,memberID AS member,
    CASE 
    WHEN svDate<>"0000-00-00 00:00:00" THEN svDate
    WHEN repeatStartDate<>"0000-00-00 00:00:00" THEN repeatStartDate
    WHEN vvStartDate<>"0000-00-00 00:00:00" THEN vvStartDate
    END
FROM services  
ORDER BY `CASE 
    WHEN svDate<>"0000-00-00 00:00:00" THEN svDate
    WHEN repeatStartDate<>"0000-00-00 00:00:00" THEN repeatStartDate
    WHEN vvStartDate<>"0000-00-00 00:00:00" THEN vvStartDate
    END` DESC

谁能告诉我如何给这个大写的语句加上dateBeg的别名，以便我可以在字段选择（SELECT id，member，dateBeg）以及ORDER BY子句（ORDER BY dateBeg）中使用dateBeg

Answer 1

您可以将CASE别名为dateBeg，如下所示；

SELECT id,memberID AS member,
CASE 
WHEN svDate<>"0000-00-00 00:00:00" THEN svDate
WHEN repeatStartDate<>"0000-00-00 00:00:00" THEN repeatStartDate
WHEN vvStartDate<>"0000-00-00 00:00:00" THEN vvStartDate
END AS dateBeg
FROM services

AS关键字通常不是必需的，因此END dateBag也应该工作。

关于ORDER BY，您现在可以使用已设置的dateBag引用。

SELECT id,memberID AS member,
CASE 
WHEN svDate<>"0000-00-00 00:00:00" THEN svDate
WHEN repeatStartDate<>"0000-00-00 00:00:00" THEN repeatStartDate
WHEN vvStartDate<>"0000-00-00 00:00:00" THEN vvStartDate
END AS dateBeg
FROM services 
ORDER BY dateBeg DESC

如何为CASE WHEN THEN SELECT语句赋予别名

1 个答案: