在更新之前删除最后一条记录

I am trying to delete the last record in the table before update it but with the current state, a new one is being inserted if there are some changes in the following fiedls route, langitude, latitude. This is a database for bus tracker app where the ride can input the desired route to get it's location displayed in the google map.

I appreciate any help.

<?php
$json = '{"latitude":74.16898451,"longitude":18.16561387,"route":13}';

$data = json_decode ( $json );

$route =   $data->{'route'};
$latitude = $data->{'latitude'};
$longitude = $data->{'longitude'};

require 'connection.php';

// check whether route's table exist.
$results = $con->query ( "SHOW TABLES like 'bus' " ) or die ( mysqli_error () );

if (($results->num_rows) == 1) {
  //"UPDATE MyGuests SET lastname='Doe' WHERE id=2"
 $sql = "REPLACE INTO bus(route, latitude, longitude)
          VALUES( ?, ? , ? )";
  $stmt = $con->prepare($sql) or die ( $con->error );
  $stmt->bind_param("sss",$route, $latitude,$longitude);
  $stmt->execute();

  $stmt->close();

  echo "Table exist";
} else {
  $create =  "CREATE TABLE bus
       (id INT(11) NOT NULL AUTO_INCREMENT PRIMARY KEY,
        route int(11) NOT NULL UNIQUE,
     latitude FLOAT(10,6) NOT NULL , 
     longitude FLOAT(10,6) NOT NULL,
     created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP)" ;
   $stmt = $con->prepare($create) or die ( $con->error );
  $stmt->execute();

  $stmt->close();

  echo "table was created";
}