我有一个包含项目数据的表，如果project_ID找不到，我想返回NULL或“ Not_Exist” 。
例如：
SELECT a.[Project ID], a.[Stage]
FROM Projects a
WHERE a.[Project ID] IN ('CR324S', 'a')
CR324S存在于表中但'a'不存在，因此我想要的结果将是：
Project ID Stage
-----------------------------
CR324S Implementation
a Not_Exist
您可以在下面尝试-
SELECT a.[pid], coalesce(b.[Stage],'Not_Exist') as stage
from
(
select 'CR324S' as pid
union
select 'a'
)A left join Projects B on A.pid=B.[Project ID] and [Project ID] IN ('CR324S','a')
要么
SELECT a.[pid], coalesce(b.[Stage],'Not_Exist') AS stage
FROM (VALUES ('CR324S'), ('a')) A(pid)
LEFT JOIN Projects B on A.pid=B.[Project ID] AND [Project ID] IN ('CR324S','a')
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