SQL INNER与DISTINCT行加入？

Question

SELECT collections.title, collections.uniqueID, uploads.uniqueID as thumb 
FROM collections 
INNER JOIN uploads ON collections.uniqueID = uploads.uploadGroup 
WHERE collections.owner = @owner 

在这种情况下，如果我有3行的“上传”具有匹配的uniqueid/uploadgroup（如在一个集合中的3个上传），这使我回3行。

我在寻找的是每行DISTINCT COLLECTIONS.UNIQUEID一行 - 这可能吗？

所以当收藏品有

1 | title | idhere 

，并上传了

1 | uniqueID1 | idhere 
2 | uniqueID2 | idhere 
3 | uniqueID3 | idhere 

我目前正在返回

1 | title | uniqueID1 
2 | title | uniqueID2 
3 | title | uniqueID3 

当所有我想要回是

1 | title | uniqueID1 

Answer 1

这里有一个方法（仅限SQL Server）：

SELECT collections.title, collections.uniqueID, uploads.uniqueID as thumb 
FROM collections 
CROSS APPLY (
    SELECT TOP 1 * 
    FROM uploads 
    WHERE collections.uniqueID = uploads.uploadGroup 
    ORDER BY uploads.uniqueID -- not required, can be changed to any column you want 
) uploads 

Answer 2

如果你需要从上传表的简单不同的列表，那么你可以做这样的：

SELECT collections.title, collections.uniqueID, uploads.uniqueID as thumb 
FROM collections 
INNER JOIN (SELECT DISTINCT uniqueID FROM uploads) uploads ON collections.uniqueID = uploads.uploadGroup 
WHERE collections.owner = @owner 

Answer 3

SELECT collections.title, collections.uniqueID, min(uploads.uniqueID) as thumb 
FROM collections 
JOIN uploads ON collections.uniqueID = uploads.uploadGroup 
WHERE collections.owner = @owner 
GROUP BY collections.title, collections.uniqueID