MySQL查询从5个表中选择联接

Question

I have 5 tables:

tag: {tagID,tagDetails}
user: {userID,userDetails,u_status=[active or banned]}
subscribe: {tagID,userID}
item: {itemID, itemDetails,i_status=[active or banned]}
item_tag: {tagID,itemID}

I want to select these data:

result: {tagID, tagDetails, num_subscribers, num_items}

For each tagID, num_subscribers is the number of users under the table user whose u_status is 'active' and whose userID and the said tagID exists in the table subscribe

For each tagID, num_items is the number of users under the table item whose i_status is 'active' and whose itemID and the said tagID exists in the table item_tag

Also, I want all the tagID to appears in the result. If there are no users subscribing or items associated with that tagID, the record will be

{tagID,tagDetails,0,0}

What is the best (as 'human readable' as possible) one nested query that produce this result?

Answer 1

Is this what you're after?

        SELECT T.tagID, T.tagDetails, count(distinct U.u_status), count(distinct I.i_status)
        FROM tag T
             JOIN subscribe S ON T.tagID = S.tagID
             JOIN user U ON S.userID = U.userID
             JOIN item_tag IT ON T.tagID = IT.tagID
             JOIN item I ON IT.itemID = I.itemID
        WHERE U.u_status = 'active' and I.i_status = 'active'
        GROUP BY T.tagID

        UNION

        (SELECT tagID, tagDetails, 0, 0
        FROM tag
        EXCEPT
        SELECT T.tagID, T.tagDetails, 0, 0
        FROM tag T
             JOIN subscribe S ON T.tagID = S.tagID
             JOIN user U ON S.userID = U.userID
             JOIN item_tag IT ON T.tagID = IT.tagID
             JOIN item I ON IT.itemID = I.itemID
        WHERE U.u_status = 'active' and I.i_status = 'active'
        GROUP BY T.tagID)

You might have to fiddle with the brackets and aliasing.