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<?php
  //$carnet_provisional = "CEG".rand(1000,10000);
  //echo $carnet_provisional;

  $servername = "localhost";
    $database = "juliojod_admisiones";
    $username = "root";
    $password = "";
    $conn = mysqli_connect($servername, $username, $password, $database);
    $conn = mysqli_connect($servername, $username, $password, $database);
	// Check connection
	if (!$conn) {
	    die("Connection failed: " . mysqli_connect_error());
	}
  /*$query_max ='SELECT MAX(carnet_provisional) FROM datos';
  $res = mysqli_query($conn, $query_max);
  while($row = mysqli_fetch_array($res)){
  	echo $row['carnet_provisional'];
  }*/

  $sql = "SELECT MAX(carnet_provisional) AS carnet FROM datos";
  $result = mysqli_query($conn, $sql);
  $row = mysqli_fetch_array($result);
	echo "resultado: ".$row['carnet'];
  // imprimimos el valor obtenido, en este caso el mayor id insertado en una tabla
  /*while($row = mysqli_fetch_array($res)){
  	echo "resultado: ".$row['carnet'];


	$sql = "
    SET @id = SELECT max(id) from tabla;
    SET @corr = SELECT max(corr) from tabla;
    INSERT INTO tabla (id, libro, asiento, correlativo, dato) 
    SELECT @id:=@id+1 as id, $libro, $valorAsto, @corr:=@corr+1 as corr, dato
    FROM tabla2;
";

$sth = $BD->prepare($sql);
$sth->execute();

  }*/
 ?>