带有DISTINCT行的SQL INNER JOIN？

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，如果我在“上传”中有3行具有匹配的uniqueid / uploadgroup（如在集合中的3个上传中），这会给我3行。

我正在寻找的是每个DISTINCT COLLECTIONS.UNIQUEID一行 - 这可能吗？

所以当收藏品有

1 | title | idhere

和上传有

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

我现在回来了

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

当我想要归还的时候

1 | title | uniqueID1

Answer 1

如果您需要上传表格中的简单不同列表，那么您可以这样做：

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 2

这是一种方法（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 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