本文介绍了引用 SELECT 列表中其他地方的别名的处理方法，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
我有以下疑问:
select FirstName, LastName,
Case
When LastName = 'Jones'
then 'N/A'
End as Other,
Case
When Other is not null
then 1
else 0 as Flag
Flag 值取决于 Other，但由于 Other 是别名，因此 Flag 字段无法识别 Other.
The Flag value depends on Other but as Other is an alias, the Flag field does not recognize Other.
我想，我可以在选择中使用选择.Flag 是否有更好的方法来识别其他别名列?
I guess, I can use a select within a select. Is there a better way for Flag to recognize the Other alias column?
推荐答案
由于解析查询的方式，您不能引用 SELECT 和 ORDER BY 之外的别名.典型的解决方法是将其隐藏在派生表中:
You can't refer to an alias outside of SELECT and ORDER BY because of the way a query is parsed. Typical workaround is to bury it in a derived table:
SELECT
FirstName, LastName, Other,
Flag = CASE WHEN Other IS NOT NULL THEN 1 ELSE 0 END
FROM
(
SELECT FirstName, LastName,
CASE WHEN LastName = 'Jones'
THEN 'N/A'
END AS Other
FROM dbo.table_name
) AS x;
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