Question

I am a little confused on the logic of how to write this SQL statement. When a user clicks on a tag, say HTML, it would display all the posts with HTML as its tag. (a post can have multiple tags)

I have three tables:

1. Posting–>posting_id, title, detail,
   etc
2. tags–>tagID, tagname
3. postingtag–>posting_id, tagID

I want to display all the title of the post and the date added.

    global $dbc;
    $tagID=$_GET['tagID']; //the GET is set by URL

    //part I need help with. I need another WHERE statment to get to the posting table
    $query = "SELECT p.title,p.date_added, t.tagname FROM posting as p, 
    postingtag as pt, tags as t WHERE t.tagID=$tagID";

   $data = mysqli_query($dbc, $query);

  echo '<table>';
  echo '<tr><td><b>Title</b></td><td><b>Date Posted</b></td></tr>';
  while ($row = mysqli_fetch_array($data)) {         
     echo '<tr><td>'.$row['title'].'</td>';
     echo '<td>'.$row['date_added'].'</td></tr>';
     }
  echo '</table>';
}

I am fairly new to mySQL so still trying to figure out the logic of it all 🙂

Answer 1

This is more clearly written using ANSI syntax:

select p.title, p.date_added, t.tagname 
from posting p
inner join postingtag pt on p.postingID = pt.postingID
inner join tags t on pt.tagID = t.tagID
where t.tagID=$tagID