Don't understand php MySQL access denied issue - mysql

Question

I am running MySQL Server version: 5.7.25-0ubuntu0.16.04.2 - (Ubuntu).
When I run this php script below with the CORRECT MySQL root user password entered I get the error:
Access denied for user 'root'#'localhost' (using password: NO)
However if I change the root user to an INCORRECT value I get the MySQL error:
Access denied for user 'root'#'localhost' (using password: YES)
I know the MySQL root user password I'm entering is correct because I can log into both the mysql command line and phpmyadmin with it.
So the CORRECT password when received by MySQL is returning access denied using password NO but I don't understand why it would do that. Any help is much appreciated.
<?php
$dbusername = "root";
$dbpassword = "password";
$dbname = "DB";
$dbtable = "table_name";
$con=mysqli_connect("localhost",$dbusername,$dbpassword,$dbname);
// Check connection
if (mysqli_connect_errno())
{
echo " " . mysqli_connect_error();
}
?>

Answer 1

Just in case anyone has the same problem, it turned out that the issue was the MySQL password I was using started with the character $. The mysql command line program and phpmyadmin had no problem with accepting this character in the password but when it was included as part of a mysqli connection string (or PDO connection string for that matter) it would throw the 1045 Access Denied Using Password: NO error.
I changed the password's first character to # and no more error.

Answer 2

Assuming you mysql / root user password is Pass123. Connect to Mysql Shell and run below sql statements.
GRANT USAGE ON *.* to `root`#`%` IDENTIFIED BY 'Pass123';
GRANT ALL PRIVILEGES ON *.* TO `root`#`%` WITH GRANT OPTION;
flush privileges;
Now update info in php and run PHP again.
<?php
$dbusername = "root";
$dbpassword = "Pass123";
$dbname = "DB";
$dbtable = "table_name";
It is recommended to create a non root user to use in the application. In my answer, I have used root as you have used this user in your question.
See create-new-user-grant-permissions-mysql
Don't forget to change database and table names.