我有以下查询:
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,Flag字段无法识别Other。
我想,我可以在选择中使用选择。 Flag有更好的方法来识别Other alias列吗?
答案 0 :(得分:5)
由于解析查询的方式,您无法引用SELECT和ORDER BY之外的别名。典型的解决方法是将其埋在派生表中:
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;
答案 1 :(得分:1)
您也可以使用公用表表达式(CTE)执行此操作:
;WITH cte AS
(
SELECT
firstname,
lastname,
CASE WHEN lastname = 'Jones' THEN 'N/A'
END AS Other
FROM @t
)
SELECT
firstname,
lastname,
CASE WHEN other IS NOT NULL THEN 1
ELSE 0
END AS Flag
FROM cte
答案 2 :(得分:0)
您必须在SELECT
中使用SELECT
:
SELECT FirstName, LastName, Other,
Case When Other is not null
then 1
else 0 END as Flag
FROM
(
select FirstName, LastName,
Case
When LastName = 'Jones'
then 'N/A'
End as Other
from yourTable
) x
或者,您可以在评估CASE
字段时重复使用Other
字段{:1}}字段:
Flag