Leaderboard

the following is a 'tricky' example of INSERTing data that satisfies a maximum count of rows - $query = "INSERT INTO team_members (team_id, staff_id, stafftype) SELECT -- the following values being SELECTed are the actual data values to insert ?,?,? FROM DUAL -- dual is an allowed dummy table name to satisfy the FROM ... WHERE syntax WHERE (SELECT COUNT(*) FROM team_members WHERE team_id = ? AND stafftype='leader') < 1 -- insert the data if the WHERE (subquery count) < 1 is TRUE"; $stmt = $pdo->prepare($query); $stmt->execute([$team_id, $staff_id, $stafftype, $team_id]); if($stmt->rowcount()) { echo "A leader row was inserted for team_id: $team_id, staff_id: $staff_id<br>"; } else { echo "A leader already exists for team_id: $team_id<br>"; } this example was to insert a maximum of one 'leader' row per team id. you would change it to insert a maximum of two rows per datetime appointment slot. because this uses a single query to both get a count of the number of existing rows and insert a new row, it will work correctly for multiple concurrent instances of your script.

DOM ids must be unique. you basically have the same problem (and solution) as in this recent thread - https://forums.phpfreaks.com/topic/315508-php-and-javascript-with-mysql-copy-button/