使用JOINING表创建mysql查询语法

Question

I'm having trouble getting some data.... I was wondering if someone can help me,

I have 4 tables (likes, follow, comment, users)

I want to be able to populate my page when a user likes/comments/follows/etc... (if a user is following a particular user).

likes

idlikes   idusers    iditem
  1          1          5
  2          2          4
  3          2          22

follow

idfollow   idusers_follower   idusers    idbusiness
  1              1               2           
  2              1               3           
  3              1               4           
  4              4               2           
  5              4                           1

comment

idcomments   idusers    text
   1            1       asfd
   2            2       safd

users

idusers
   1
   2
   3
   4

For example if I am id user #1, I'm following users #2, #3, #4

My page would populate to show:

• #2 likes item #4, #22.
• #4 is following #2 (because I'm following #4, this is why its showing)
• #2 comments "safd"

I'm not sure what is the best way to display this? I currently have multiple functions querying on table at a time, and I'm working on merging the arrays together? Or should I use join tables? Which I'm trying now...

Get users that I'm following.

$feeds = new feed();
$meID = 1;
$query = "SELECT idusers FROM follow WHERE iduserse_follower = ?";

$users = $dbh -> prepare($query);
$users -> execute(array($meID));

while($following = $users -> fetch(PDO::FETCH_ASSOC)){
      $follow = $following['idusers']; //This will get all of useres I'm following
      $populate = $feeds->feed_all($follow); // from function
}

Query

class feed()
{
     public function feed_all($idusers)
     {
         // SYNTAX HELP //////////////////////
           $query = "SELECT 
           f.idusers_follower, 
           f.idusers, 
           l.iditem, 
           c.text 
           FROM follow f, users u 
           JOIN likes l 
           ON l.idusers = f.idusers 
           JOIN comment c
           ON c.idusers = f.idusers
           WHERE f.idusers_follower = ? AND f.idusers_follower = l.idusers AND f.idusers_follower = c.idusers AND f.idusers = u.idusers"

           $pop = $dbh->prepare($query);
           $pop ->execute($idusers);

           // while loop to return value
    while($row = $pop -> fetch(PDO::FETCH_ASSOC))
    {
        $feed_data[]=$row;
    }
    return $feed_data;
     }
}

This is where I'm stuck. :( I'm not even sure if I'm doing the statement right?

++++++++++ EDIT: ++++++++++++

I have edited to add idbusiness

Now since I'm following #4, it would also show up that #4 is following #1.

Answer 1

Your current approach of performing three separate queries is as good as any; you can combine them into a single resultset using UNION , which would be useful if you wanted to sort the combined results by some field (eg activity timestamp) and/or limit the combined results:

  SELECT idusers, 'likes' AS what, likes.iditem AS detail
  FROM   likes JOIN follow USING (idusers)
  WHERE  follow.idusers_follower = 1

UNION ALL

  SELECT f1.idusers, 'follows', f2.idusers
  FROM   follow f1 JOIN follow f2 ON f1.idusers = f2.idusers_follower
  WHERE  f1.idusers_follower = 1

UNION ALL

  SELECT idusers, 'commented', comment.text
  FROM   comment JOIN follow USING (idusers)
  WHERE  follow.idusers_follower = 1

See it on sqlfiddle .