MySQL用户订阅查询失败

Question

I have a database named socialnetwork and has 5 tables category , post_category , posts , subscribe , user .

my table structures

     --------                       -------------
     category                       posts  
     --------                       ------------
     categoryID                     postID 
     categoryName                   post
                                    userID
                                    categoryID

   --------------                ---------------         
    post_category                subscribe
   ---------------               ---------------
    postID                       subscriberID  
    categoryID                   categoryID

  --------------
   usertable
  --------------
   userID
   userName

data's in the table

category table                              usertable
--------------------------               -------------------
categoryID     categoryName               userID      userName
---------------------------              --------------------
1                film                      1    jijojohn32
2               television                 2    sijojohn                                 


posts_category table                     subscribe table
------------------                      -------------------------
postID     categoryID                    subscriberID    categoryID
---------------------                   ------------------------
1            1                            1                1
1            2                            1                2     
2            2                            2                2                 


 posts table
---------------------------------------------------
 postID       post             userID     categoryID
 --------------------------------------------------
 1         this post is cool    1           1
 2           demo post          2           2

User 1 can subscribe to different categories and he can see the articles in the categories he subscribes. That's what i am trying to implement here. And i have this query but it's not giving me the result i want.

USE socialnetwork;
SELECT  socialnetwork.usertable.userName,socialnetwork.posts.post, GROUP_CONCAT(socialnetwork.category.categoryName) as category
FROM socialnetwork.category
INNER JOIN subscribe
ON subscribe.categoryID = category.categoryID
INNER JOIN posts
ON posts.categoryID = subscribe.categoryID
INNER JOIN usertable
ON usertable.userID = posts.userID
INNER JOIN socialnetwork.post_category
ON post_category.postID = posts.postID

WHERE subscriberID = "1"
GROUP BY socialnetwork.category.categoryName

Here's the result i am getting

 ---------------------------------
    username       post            category
    ----------------------------------
   jijojohn32  this post is cool   film, film
    sijojohn   demo post           television

The result i want

 ---------------------------------------------
    username       post               category
    -------------------------------------------
   jijojohn32  this post is cool     film,television
    sijojohn   demo post              television

I want the post from the categories he subscribed to , the username of the user posted the articles , and categories which posts reside. What's wrong in my query ?. any idea ?. thanks

Answer 1

You are not aggregating by the right columns. I think this is the query that you want:

SELECT ut.userName, p.post, GROUP_CONCAT(c.categoryName) as category
FROM socialnetwork.category c INNER JOIN
     subscribe s
     ON s.categoryID = c.categoryID INNER JOIN
     posts p
     ON p.categoryID = s.categoryID INNER JOIN
     usertable ut
     ON ut.userID = p.userID INNER JOIN
     socialnetwork.post_category pc
     ON pc.postID = p.postID
WHERE subscriberID = 1
GROUP BY ut.userName, p.post;

Answer 2

There exists a conflict

Category table consists of

Category id and Category Name

Post Table consists of

Post id and Corresponding Category Id

As well as

Post_Category table consists of

Post id and Category Id

Hence it is picking from the Posts table , that Row 1 - has only 1 category id associated with it

I suggest you remove Category id from Post table

It is pointless to have 2 keys in 1 table, and similar 2 keys in other table.

Try to establish Primary key Foreign key relationship.

Hope that helps

Answer 3

Here's the working query. I made some modifications in the table. Deleted the categoryID from posts. Made a new table called post_category.

--------------
post_category
-------------
postID
categoryID

Here's the query

SELECT GROUP_CONCAT(category.categoryName) as category  , category.categoryID , subscribe.subscriberID , posts.post ,
  usertable.userName

from category

INNER JOIN subscribe
ON subscribe.categoryID = category.categoryID


INNER JOIN post_category
ON category.categoryID = post_category.categoryID

INNER JOIN posts
ON posts.postID =  post_category.postID

INNER JOIN usertable
ON usertable.userID = posts.userID

WHERE subscriberID = 1
GROUP BY post_category.postID