I GET "No database selected" ERROR even that is selected - php

Question

Im new in MySql and PHP and im trying to make a CRUD but everytime i try to insert data into table called "studenti" i get the error that i didnt select a database but i selected a database with mysqli_select_db($con, "d_base");
Somebody please help me cuz i dont understand why its not workin'
Here is the code;
$id = $_POST['ID'];
$nota = $_POST['Nota'];
$emri = $_POST['Emri'];
$mbiemri = $_POST['Mbiemri'];
$servername = "localhost";
$dbname = "d_base";
// 1.Create connection
$con = mysqli_connect("localhost","d_base");
// Check connection
if (mysqli_connect_errno())
{
echo "Failed to connect to MySQL: " . mysqli_connect_error();
}
if (!mysqli_query($con,"INSERT INTO studenti (id, nota, emri, mbiemri) VALUES ('$id', '$nota','$emri','$mbiemri')"))
{
echo("Error description: " . mysqli_error($con));
}
// Perform queries
mysqli_select_db($con, "d_base");
mysqli_query($con,"INSERT INTO studenti (id, nota, emri, mbiemri) VALUES ('$id', '$nota','$emri','$mbiemri')");
mysqli_close($con);

Answer 1

Before all that if you are a begginer go straight on PDO or use mysqli with prepared statements its safer.
Here is example how your php and html form must look like and work.
First you must check if submit button is pressed, if its pressed read values form form $_POST variables.
Second thing you must escape injection to your mysql by using function mysqli_real_escape_string().
After that try to insert query and check for error, if there is no error query will be inserted successfully.
PHP code
<?php
// set error report ; 1 = on | 0 = off
error_reporting(1);
$db_host = "localhost"; // host
$db_user = "root"; // database username
$db_pass = ""; // database password
$db_name = "d_base"; // database name
// 1.Create connection
$con = mysqli_connect($db_host, $db_user, $db_pass, $db_name);
// Check connection
if (mysqli_connect_errno())
{
echo "Failed to connect to MySQL: " . mysqli_connect_error();
}
// if form is submited
if (isset($_POST['submit']))
{
// escape post variables
$id = mysqli_real_escape_string($con, $_POST['ID']);
$nota = mysqli_real_escape_string($con, $_POST['Nota']);
$emri = mysqli_real_escape_string($con, $_POST['Emri']);
$mbiemri = mysqli_real_escape_string($con, $_POST['Mbiemri']);
// make query
$query = mysqli_query($con, "INSERT INTO studenti (id, nota, emri, mbiemri VALUES ('$id', '$nota', '$emri', '$mbiemri')")
// check for query
if (!$query)
{
echo "Error description: " . mysqli_error($con);
}
else
{
echo "Query inserted.";
}
// close connenction
mysqli_close($con);
}
?>
<form action="" method="post">
<input type="text" name="ID" placeholder="Id"><br />
<input type="text" name="Nota" placeholder="Nota"><br />
<input type="text" name="Emri" placeholder="Emri"><br />
<input type="text" name="Mbiemri" placeholder="Mbiemri"><br />
<input type="submit" name="submit" value="Submit form">
</form>