如何在SQL中实现回退语言概念

Question

我有一个具有不同语言记录的场景，我需要的是获取单个行中的所有数据，如果某些数据不是必需的语言，则下一个默认语言进入该记录的操作，依此类推。

declare @LanguageId int = 3
    select * from Purpose where LanguageId=(CASE WHEN @LanguageId = 1 THEN CASE WHEN EXISTS
    (SELECT PurposeId
    FROM Purpose
    WHERE LanguageId = @LanguageId) THEN @LanguageId WHEN EXISTS
    (SELECT PurposeId
    FROM Purpose
    WHERE LanguageId = 2) THEN 2 ELSE 3 END WHEN @LanguageId = 2 THEN CASE WHEN EXISTS
    (SELECT PurposeId
    FROM Purpose
    WHERE LanguageId = @LanguageId) THEN @LanguageId WHEN EXISTS
    (SELECT PurposeId
    FROM Purpose
    WHERE LanguageId = 1) THEN 1 ELSE 3 END WHEN @LanguageId = 3 THEN CASE WHEN EXISTS
    (SELECT PurposeId
    FROM Purpose
    WHERE LanguageId = @LanguageId) THEN @LanguageId WHEN EXISTS
    (SELECT PurposeId
    FROM Purpose
    WHERE LanguageId = 2) THEN 2 ELSE 1 END END) 

我已经进行了查询并且工作正常，我正在寻找替代的替代优化查询。欢迎任何帮助或建议。

Answer 1

这可能对您有用：

SELECT
p1.PurposeId, MIN( ISNULL( p2.LanguageId, p1.LanguageId ) ) AS LanguageId
FROM Purpose p1
LEFT OUTER JOIN Purpose p2 on p1.PurposeId = p2.PurposeId AND p2.LanguageId = :desiredLanguage
GROUP BY p1.PurposeId

如果有条目，则产生desiredLanguage，或者每个PurposeId产生最低的可用LanguageId。