如果成功声明ajax

I'm having trouble implementing if statement in ajax success function.

<?php  
  include('../Config/config.php');
  $myquery = "SELECT * FROM voters WHERE Precinct = '".$_POST['precinct']."'";
  $execute = mysqli_query($mysqli, $myquery);
  if (mysqli_num_rows($execute) >= 1)
  {
    echo "Precinct is full.
 Recheck precinct number.";
  }
?>

function checkerprecinct() {
  var precinct = $("#precinct").val();
  $.ajax({
    type: "POST",
    url: "precinctchecker.php",
    data: "precinct=" + precinct,
    success: function(data) {
      console.log(data);
      if (data === "") {
        alert("Data is empty!");
      } else {
        alert(data);
      }
    }
  });
}

I would like to use this as a validation.
I want to alert the user if the sent data contains similar data from the database.

try this code

change with your code

PHP Code:

$data = array();
if (mysqli_num_rows($execute) >= 1)
{
    $data= array('code'=>100,'message'=>"Precinct is full.
 Recheck precinct number.");
    //echo "Precinct is full.
 Recheck precinct number.";
}else{
    $data= array('code'=>101,'message'=>"Data is empty!");
}

echo json_encode($data);
exit;

ajax code:

var data = JSON.parse(data);
if (data['code'] == 100) {
    alert(data['message']);
}