limit entry to db while added new records - php

Question

ok i have this recent visits table and the following code i use to enter records into the table user wise
if($user->is_logged_in() ){
$postid = $row['postid'];
$uid = $_SESSION['memberid'];
$stmt = "SELECT * FROM recent WHERE postid = :postid AND memberid = :memberid";
$stmt = $db->prepare($stmt);
$stmt->bindParam(':postid', $postid, PDO::PARAM_STR);
$stmt->bindParam(':memberid', $uid, PDO::PARAM_STR);
$stmt->execute();
$recentCount = $stmt->rowCount();
if(!$recentCount)){
$stmt = $db->prepare('INSERT INTO recent (postid,memberid) VALUES ( :postid,:memberid)');
$stmt->execute(array(
':postid' => $postid,
':memberid' => $uid
));
}
}
but the thing is i wish to limit records, as in per user only 50 records should be in db. supposing user visits a new topic then if there already 50 records in recent table for the user then the number 50 gets deleted and 49 record becomes 50. i hope you get my point?
its just that records per user should not exceed above 50 is what i mean.

Answer 1

Based on the question and comments, I think you can do it like this (you didn't mention the name of your date field but for this example I'll assume it's called createddate):
if($user->is_logged_in() ){
$postid = $row['postid'];
$uid = $_SESSION['memberid'];
$stmt = "SELECT COUNT(*) FROM recent WHERE postid = :postid AND memberid = :memberid"; //let mysql count the rows
$stmt = $db->prepare($stmt);
$stmt->bindParam(':postid', $postid, PDO::PARAM_STR);
$stmt->bindParam(':memberid', $uid, PDO::PARAM_STR);
$stmt->execute();
$recentCount = $stmt->fetchColumn(); //fetch first column in first row, this will be the count result
if($recentCount >= 50)
{
$stmt2 = $db->prepare('DELETE FROM recent WHERE createddate = (select min(createddate) where memberid = :memberid)');
$stmt2->bindParam(':memberid', $uid, PDO::PARAM_STR);
$stmt2->execute();
}
$stmt = $db->prepare('INSERT INTO recent (postid,memberid) VALUES ( :postid,:memberid)');
$stmt->execute(array(
':postid' => $postid,
':memberid' => $uid
));
Apologies if the PDO syntax is wrong, I haven't used it in a while. I'm sure you can make that right yourself. But the important thing is the structure of the PHP "if" statement and the "delete" SQL.