按平台选择和计算不同的活动用户，并比较它们是否存在于其他表中

Question

I have about six(6) tables each linked with userid. One of the tables is userinfo. The user info contains user details including their store platform(eg magento)

1. Userinfo contains both active and non-active users (active users have created at least one activity in the other 5 tables).
2. I want to count distinct number of users in the userinfo with platform of magento who have records in any of the other tables.
3. Currently I am able to count distinct number of users in the other five tables with the ff code but want to join this with the userinfo table so I can select active users with platform magento.
4. Without adding the userinfo table means I have no way of selecting users by platform.

5. Selecting users in userinfo table only, with platform of magento will be easy, but that means I may select users who only register but do not go on to create activity on my app.

        $query3 = ("SELECT   COUNT(*)
        FROM     (
          SELECT userid FROM table1
          UNION SELECT userid FROM table2
          UNION SELECT userid FROM table3
          UNION SELECT userid FROM table4
          UNION SELECT userid FROM table5
          ) AS UserIDs");
          $result3 = mysql_query($query3) or die(mysql_error()); 
          $row3 = mysql_fetch_row($result3);
          echo "Number of distinct users in all tables  = ".$row3[0] ."<br />";
   
   
     **Table 1**
     Id    userid    name   adresss
   
     **Table 2**
     Id  Title   Sex   userid
   
     **Table 3**
     Id   userid   amount
   
     **Table 4**
     Id  price  promotion  userid   productid
   
     **Table  5**
     Id  userid   category   tax   weight
   
     **userinfo**
     Id  userid   username   password   platform
   

Answer 1

Expanding on the UNION subselect from my other suggestion, you can JOIN this with the UserInfo table and get your distinct count.

SELECT   COUNT (DISTINCT ui.UserID))
FROM     (
           SELECT UserID FROM Table1
           UNION SELECT UserID FROM Table2
           UNION SELECT UserID FROM Table3
           UNION SELECT UserID FROM Table4
           UNION SELECT UserID FROM Table5
         ) AS id
         INNER JOIN UserInfo ui ON ui.UserID = id.UserID
WHERE    ui.Platform = 'Magento'