Question

i want to select the most recent entry from a table and see if that entry is exactly the same as the one the user is trying to enter. How do I do a query to “select * from the most recent entry of ‘posting'”?

    $query="Select * FROM 
        //confused here 
 (SELECT * FROM posting ORDER BY date_added DESC)
 WHERE user_id='{$_SESSION['user_id']}'
 AND title='$title'
 AND price='$price'
 AND city='$city'
 AND state='$state'
 AND detail='$detail'
 ";

 $data = mysqli_query($dbc, $query);
 $row = mysqli_fetch_array($data);
 if(mysqli_num_rows($data)>0)
 {
  echo "You already posted this ad. Most likely caused by refreshing too many times.";
  echo "<br>";
  $linkposting_id=$row['posting_id'];
  echo "See the <a href='ad.php?posting_id=$linkposting_id'>Ad</a>";
 }
 else
 {
        ...insert into the dbc
        }

//would this query work? or how do i use it to select the last ID in the table 'posting'?
    $query="SELECT LAST_INSERT_ID(posting)
     WHERE user_id='{$_SESSION['user_id']}'
     AND title='$title'
     AND price='$price'
     AND city='$city'
     AND state='$state'
     AND detail='$detail'
     ";

Answer 1

The orderby piece needs to come at the end of your query. So the query you’re asking for is something like this:

select * from posting where .... order by date_added desc limit 1;

Single-use form tokens can help prevent duplicate submissions, too.