多例语句中的别名列名 [英] Alias Column name in mutiple case statement
本文介绍了多例语句中的别名列名的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
我正在尝试使用case语句检索别名列的值.
I am trying to retrieve a value for a alias column using case statement.
CASE
WHEN FieldA = 'TestA' THEN FieldA1
WHEN FieldB = 'TestB' THEN FieldB1
ELSE NULL
END AS Alias1
但是当我尝试使用该别名来获取另一个别名的值时,出现错误
But when I try to use this alias to retrievce value for another alias , I am getting an error
CASE
WHEN Alias1 = FieldA1 THEN FieldA0
WHEN Alias1 = FieldB1 THEN FieldA1
ELSE NULL
END AS Alias2
我收到的错误消息是:
您能建议一种消除错误的方法或任何满足我要求的替代方法
Can you suggest a way to get rid of the error or any alternative approach which fulfills my requirements
推荐答案
您不能在同一SELECT
子句中使用列别名.您有两种选择:
You can't use column aliases in the same SELECT
clause. You have two choices:
使用子查询:
SELECT Alias1,
CASE
WHEN Alias1 = FieldA1 THEN FieldA0
WHEN Alias1 = FieldB1 THEN FieldA1
ELSE NULL
END AS Alias2
FROM (
SELECT CASE
WHEN FieldA = 'TestA' THEN FieldA1
WHEN FieldB = 'TestB' THEN FieldB1
ELSE NULL
END AS Alias1,
FieldA1
FieldB1
...)
,或者您可以重复在第一个CASE
中使用的逻辑:
or you can repeat the logic that you used in the first CASE
:
SELECT CASE
WHEN FieldA = 'TestA' THEN FieldA1
WHEN FieldB = 'TestB' THEN FieldB1
ELSE NULL
END AS Alias1,
CASE
WHEN FieldA = 'TestA' THEN FieldA0
WHEN FieldB = 'TestB' THEN FieldB0
ELSE NULL
END AS Alias2
这篇关于多例语句中的别名列名的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!
查看全文