Unable to Pass Data Into DB Using AJAX - php

Question

I'm trying to save some data into db using AJAX.It says it's successfully done but nothing happens.No data is being saved.Just keeps saying "Success".
index.php // form
<div id="cont">
<div id="kayit" style="display:none;">
Success
</div>
<div id="basarisiz" style="display:none;">
Empty or Fail
</div>
<form method="post" id="yaz" onsubmit="return false">
<input type="text" name="title" id="baslik" placeholder="Başlık" required><br/>
<textarea name="content" ></textarea><br/>
<input type="submit" name="gonder" value="Gönder" id="gonder" onclick="kayit()">
</form>
yaz.js
function kayit()
{
var baslik = $("input[name=title]").val();
var icerik = $("input[name=content]").val();
if (baslik =="" || icerik == "")
{
$('#basarisiz').show(1);
$('#kayit').hide(1);
}else
{
$.ajax ({
type: "POST",
url: "yazikaydet.php",
data: $("#yaz").serialize(),
success: function (sonuc) {
if (sonuc == "hata") {
alert ("unable to connect to db");
}else {
$('#kayit').show(1);
$('#basarisiz').hide(1);
$("input[name=title]").val("");
$("input[name=content]").val("");
}
}
}) }}
yazikaydet.php //the file which will save the data,not processing
<?php
include 'giris.php'; //sessions and connection strings
if(isset($_POST["gonder"]))
{
$baslik = $_POST["title"];
$icerik = $_POST["content"];
$tarih = date("d/m/20y");
$kull = $_SESSION["username"];
$kaydet = mysqli_query($connect,"INSERT INTO gonderiler (yazar,tarih,baslik,icerik) VALUES ('$kull','$tarih','$baslik','$icerik')");
if($kaydet)
{
echo "Yes";
}
else
{
echo "No";
}
}
?>