SQL INNER與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 

在這種情況下，如果我有3行的「上傳」具有匹配的uniqueid/uploadgroup（如在一個集合中的3個上傳），這使我回3行。

我在尋找的是每行DISTINCT COLLECTIONS.UNIQUEID一行 - 這可能嗎？

所以當收藏品有

1 | title | idhere 

，並上傳了

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 

當所有我想要回是

1 | title | uniqueID1 

Answer 1

這裏有一個方法（僅限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

如果你需要從上傳表的簡單不同的列表，那麼你可以做這樣的：

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