数据库上的重复数据

Question

When i click on submit button,in database at a time two data saved one is duplicate.I show my code below

<?php
if (isset($_POST['submit'])) {
    function email_subscription($data)
    {
        $db_connect = mysqli_connect('localhost', 'root', '');
        if ($db_connect) {
            $db_select = mysqli_select_db($db_connect, 'db_seip_php28');

            if ($db_select) {
                echo "Database Selected";
            } else {
                echo "Database Not Selected";
            }
        } else {
            die('Connection Fail' . mysqli_error($db_connect));
        }

        $sql = "INSERT INTO db_newsletter(email_address) VALUES ('$data[email_address]')";

        mysqli_query($db_connect, $sql);
        if (mysqli_query($db_connect, $sql)) {
            echo "  Email address save successfully";
        } else {
            echo "Sorry May be some error happen";
        } 


    email_subscription($_POST);
} ?>

Answer 1

You execute the query 2 times!

    mysqli_query($db_connect, $sql);       
    if (mysqli_query($db_connect, $sql))