Getting related tags from SQL Server when you have filtered down

Question

I asked this question before and got a great working answer.

what is the query to get "related tags" like in stack overflow

but i realized that SOF ac

Answer 1

I'd use something like this as the first version. @FirstTagID and @SecondTagID must be sorted by ID. You can query on more tags by adding more joins to the inner query.

SELECT tagName
FROM tags
WHERE id IN (
    SELECT tagID
    FROM tagsBridge
    WHERE linkID IN (
        SELECT t1.linkID
        FROM
            tagsBridge t1
            JOIN tagsBridge t2 ON t2.linkID=t1.linkID AND t2.tagID > t1.tagID
        WHERE t1.tagID=@FirstTagID AND t2.tagID=@SecondTagID
    )
    AND tagID!=@FirstTagID AND tagID!=@SecondTagID
)

Or if you want to include the number of links:

SELECT t.tagName, count(*)
FROM 
    tags t
    JOIN tagsBridge tb ON tb.tagID = t.id
WHERE
    tb.linkID IN (
        SELECT t1.linkID
        FROM
            tagsBridge t1
            JOIN tagsBridge t2 ON t2.linkID=t1.linkID AND t2.tagID > t1.tagID
        WHERE t1.tagID=@FirstTagID AND t2.tagID=@SecondTagID
    )
    AND t.tagID!=@FirstTagID AND t.tagID!=@SecondTagID
GROUP BY t.tagName

The same for three tags:

SELECT t.tagName, count(*)
FROM 
    tags t
    JOIN tagsBridge tb ON tb.tagID = t.id
WHERE
    tb.linkID IN (
        SELECT t1.linkID
        FROM
            tagsBridge t1
            JOIN tagsBridge t2 ON t2.linkID=t1.linkID AND t2.tagID > t1.tagID
            JOIN tagsBridge t3 ON t3.linkID=t2.linkID AND t3.tagID > t2.tagID
        WHERE t1.tagID=@FirstTagID AND t2.tagID=@SecondTagID AND t3.tagID=@ThirdTagID
    )
    AND t.tagID!=@FirstTagID AND t.tagID!=@SecondTagID AND t.tagID!=@ThirdTagID
GROUP BY t.tagName