从一个表中提取数据并对照另一张表进行检查，然后显示匹配项

Question

Here is the situation. I have joins everywhere in other parts of the site and everything works fine, just this one hiccup that has been driving me crazy. It is probably simple and I am just missing something.

This is a system where users can log in and follow each others blogs.

The Database Each Table has different amount of Columns and none of the Columns use the same name.

Table1 = userdetails (uses ID as Primary ID)

Table2 = blogs (uses BlogID as Primary ID) - it has BlogID, WriterID blogtitle, blogtext, blogdate, etc. as rows

Table3 = blogFollowers (uses FollowingBlogID as primary ID) this is the tan;e that keeps all info on who is following which blogs. - it has FollowingBlogID, TheBlogID, ImFollowing, FollowOrNot - FollowOrNot has to be either 0 or 1 - 0 equals Following 1 equals Not Following)

EXPLANATION User is logged in. $LoggedInUser = id of person who is logged in when they are logged in. SESSION

A logged in user want to StartFollowing a blog. The user clicks on the StartFollowing blog link. This sends info to be inserted into Table3. It creates a new row (assigns a unique id) and inserts TheBlogId (is the same as BlogID from table1) ImFollowing (inserts LoggedInUser) and FollowOrNot it inserts a 0.

EXAMPLE

1. User1 is logged in and creates BlogA.
2. User2 logs in and sees it at the top of the Blogs page.
3. User2 wants to StartFollowing this blog.
4. User2 clicks the link. It inserts the info from above into table 3.
5. User2 then refreshes the page. Now instead of saying StartFollowing it says StopFollowing.

The Problem : So what I cannot figure out.

When logged in the user sees a list of all blogs-Blog Page (From Table2) on the page. Next to each blog title there is a link that says StartFollowing (the logged in user is NOT following this blog) or StopFollowing (the logged in user IS following this blog). How can I make this happen. No matter what I try I either just show the Logged in user's blogs that they already follow OR i see only the blogs that are being followed (table3).

Answer 1

So here is my take on it:

First , you said

A logged in user want to StartFollowing a blog. The user clicks on the StartFollowing blog link. This sends info to be inserted into Table3. It creates a new row (assigns a unique id) and inserts TheBlogId (is the same as BlogID from table1 ) ImFollowing (inserts LoggedInUser) and FollowOrNot it inserts a 0.

Shouldnt it be table2 (the bold one).

Second : The table3 should have a composite primary key based on the blogId and userId . Only then will it be logical as a user can follow many blogs.

Third , to answer your question:

No matter what I try I either just show the Logged in user's blogs that they already follow OR i see only the blogs that are being followed (table3).

This is the general pseudocode:

foreach( $allRowsOfTable2 as $row) { //each row for those blogs being displayed on page.
blogId = $row['blogId'];
blogAuthorId = $row['blogAuthorId'];

  if( blogAuthorId != currentLoggedInUserID ) { //obviously why do you need to follow yourself right? :P
     $sql = "SELECT * from table3 WHERE blogId=`$blogId` AND userId='$currentLoggedInUserID';";
     $result = do_a_database_operation_here;
     if(count($result) >0 ) { //yes he is following the blog
          //display the "unfollow" link
     }
     else {
          //display the "follow" link
     }
  }
}

PS: You can do this in a better way if you can use joins in sql. If you provide the codes to your table structure a query can be shown.