PHP not submitting form data without echo statement? [duplicate] - php

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During a test to see if my database would receive a username through a form field , the code would not work unless I echo'd out error messages. Why is this? My goal is to send the username through the form field , and retrieve the list of usernames on the same page below the form field.
My html for submitting usernames ,
<section id="banner">
<div class="content">
<header>
<h2>Add Usernames Here</h2>
<form method="post">
<br><input type="text" name="user_name"><br>
<input type="submit" value="Submit">
</form>
</header>
</div>
For displaying usernames:
<section id="five" class="wrapper style2 special fade">
<div class="container">
<header>
<h2>Added Usernames</h2>
<?php require 'post.php'; ?>
</header>
</div>
</section>
And my post.php code
<?php
//connection
$url = parse_url(getenv("CLEARDB_DATABASE_URL"));
$server = $url["host"];
$username = $url["user"];
$password = $url["pass"];
$db = substr($url["path"], 1);
$conn = new mysqli($server, $username, $password, $db);
//test connection
if(!$conn)
{
echo 'not connected';
}
if(!mysqli_select_db($conn,'heroku_cd6b3866e127c21'))
{
echo 'database not selected';
}
//insert username
$user_name = $_POST['user_name'];
$sql = "INSERT INTO store (user_name) VALUES ('$user_name')";
//test query
if(!mysqli_query($conn,$sql))
{
echo 'not inserted';
}
else {
echo 'inserted';
}
//echo all usernames
mysqli_select_db($db,$conn);
$sql2 = "SELECT * FROM store";
$mydata = mysqli_query('$sql2,$conn');
while($record = mysqli_fetch_array($mydata)){
echo "<br>";
echo $record['user_name'];
}
?>
This code works until I remove the if statements , checking for the connection.

Answer 1

This is simple example, only one page named index.php:
<form action="index.php" method="post">
<br><input type="text" name="user_name">
<br><input type="submit" value="Submit">
</form>
<?php
$username = $_POST["user_name"];
$link = mysqli_connect("127.0.0.1", "root", "", "db12");
mysqli_query($link, "INSERT INTO users (username) values ('$username')");
echo $username;
$query = "SELECT username FROM users";
$result = mysqli_query($link, $query);
/* fetch associative array */
while ($row = mysqli_fetch_array($result)) {
echo $row['username'] . "<br>";
}
/* close connection */
mysqli_close($link);
?>
In production app always write separate page for insert, and always use prepare http://php.net/manual/en/mysqli.prepare.php

Answer 2

You aren't running the query anywhere else except in those if statements.
Try adding $mysqli->query($sql) underneath your declaration of $sql

Answer 3

You still need to call these functions:
mysqli_select_db($conn,'heroku_cd6b3866e127c21')
and
mysqli_query($conn,$sql)
Even if they are wrapped in an if statement or not you still need to select the db and send it a query. But I wouldn't want to do it like this, I would look into PDO.
http://php.net/manual/en/book.pdo.php
These methods are known for having SQLi vulnerabilities.
Edit
Also this line has an error:
$mydata = mysqli_query('$sql2,$conn');
I assume it should be:
$mydata = mysqli_query($conn,$sql2);