MySQL查詢選擇從5桌

Question

加入我有5個表：

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} 

我想選擇這些數據：

result: {tagID, tagDetails, num_subscribers, num_items} 

對於每個標籤識別，NUM_SUBSCRIBERS是用戶的桌子底下數用戶，其u_status爲'active'且其用戶ID和所述標籤ID存在於表中訂閱

對於每個tagID，num_items是i_status爲'active'的表項下的用戶數量，以及其itemID和所述tagID存在於表中item_tag

此外，我希望所有的tagID出現在結果中。如果沒有與該標籤識別關聯的用戶訂閱或項目，該記錄將被

{tagID,tagDetails,0,0} 

是什麼產生這種結果的最好（如「人類可讀」越好）一個嵌套查詢？

Answer 1

這是你所追求的？

 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) 

您可能不得不剔除括號和別名。