如何在SQl Server 2008中选择独特但只有一个领域是多个领域？

Question

我有一个查询：

SELECT Content.content_name, Language2.Name, Language2.language_id, 
Content.id, Content.content_description, 
FROM Language AS Language2 
LEFT JOIN contents AS Content ON (Language2.language_id = Content.language_id) 

如何只选择不同CONTENT_NAME？

Answer 1

你这样做：

SELECT DISTINCT Content.content_name 
FROM Language AS Language2 
LEFT JOIN contents AS Content ON (Language2.language_id = Content.language_id) 

那么，为什么这不回答你的问题？

让我们看看下面的数据（只是前两列）：

content_name  Name 
XXXXX   1234 
XXXXX   5678 

SELECT DISTINCT意味着你只需要一个行，但你要为名称什么？

你需要做的是重新编写代码来使用GROUP BY和挑选其他列相应的聚合函数：

SELECT 
    Content.content_name, 
    MIN(Language2.Name) AS Name, 
    MIN(Language2.language_id) AS language_id, 
    MIN(Content.id) AS id, 
    MIN(Content.content_description) AS content_description, 
FROM 
    Language AS Language2 
    LEFT JOIN contents AS Content 
     ON (Language2.language_id = Content.language_id) 
GROUP BY 
    Content.content_name 

现在，很有可能这不会产生你想要任何东西，但有一点是确实，你不能欺骗数据库引擎“只选择一行返回，我不关心哪一行”。

Answer 2

你的意思是像下面

SELECT Content.content_name, 
FROM Language AS Language2 
LEFT JOIN contents AS Content ON (Language2.language_id = Content.language_id) 
Group by Content.content_name 

Answer 3

WITH q AS 
     (
     SELECT Content.content_name, Language2.Name, Language2.language_id, Content.id, Content.content_description, ROW_NUMBER() OVER (PARTITION BY content_name ORDER BY language_id) AS rn 
     FROM Language Language2 
     LEFT JOIN 
       Contents AS Content 
     ON  Language2.language_id = Content.language_id 
     ) 
SELECT * 
FROM q 
WHERE rn = 1