data is not insert to my database table - php

Question

<?php
$con = mysqli_connect('localhost','root','');
if(!$con)
{
echo 'not connected to server';
}
if(!mysqli_select_db($con,'user_table'))
{
echo 'database not selected';
}
$mobilenumber = $_POST['mobilenumber'];
$operator = $_POST['operator'];
$state = $_POST['state'];
$sql = "INSERT INTO user_details (mobilenumber,operator,state) VALUES ('".$mobilenumber."','".$operator."','".$state."')";
if(!mysqli_query($con,$sql))
{
echo 'not inserted';
}
else
{
echo 'inserted';
}
//$select="insert into user_details (mobilenumber,operator,state) VALUES ('".$mobilenumber."".$operator."".$state."')";
//$sql=mysql_query($select);
//print '<script type="text/javascript">';
//print 'alert("the data is inserted.....")';
//print '<script>';
//mysql_close();
?>
<form method="post" action="insert.php" id="submitForm">
<select id="operator" type="select" ng-model="operatorName" ng-class="operatorError ? 'error-border':''" autocomplete="off" placeholder="Select operator" ng-click="showOperators($event);" name="operator" method=POST action=/insert.php class="form-control fetchoperators drpdwn-arrow ng-pristine ng-valid ng-touched" required>
<select name="state" class="state" id="state" required name="state" method="post" action="insert.php">

Answer 1

The Simplest way is to try to debug your query.
What i would have done is simply the process as much as i could firt.
do echo $sql;
Then copy the result and paste it in the my sql server if that works.
Then check your connection object apparently it's look right but the best way of doing this copy the following code. and try this
<?php
$servername = "localhost";
$username = "root";
$password = "";
$dbname = "user_table";
// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);
// Check connection
if ($conn->connect_error) {
die("Connection failed: " . $conn->connect_error);
}
$sql = "INSERT INTO user_details (mobilenumber,operator,state) VALUES ('".$mobilenumber."','".$operator."','".$state."')";
if ($conn->query($sql) === TRUE) {
echo "New record created successfully";
} else {
echo "Error: " . $sql . "<br>" . $conn->error;
}
$conn->close();
?>
change the credentials and check the response and paste it in the comments then we will go along.

Answer 2

you should use
mysqli_query($con,$sql) or die((mysql_error());
it will show you error for which it is not inserting data in you table