php - Access denied for user 'my_user'@'localhost' (using password: YES) -

can explain means , can fix it?

the error:

access denied user 'my_user'@'localhost' (using password: yes)

my php file:

<?php     $mysqli = new mysqli("localhost", "my_user", "my_password", "my_db");      $password = $_post["password"];     $username = $_post["username"];      $statement = mysqli_prepare(mysqli, "select * user username = ? , password = ?");     mysqli_stmt_bind_param($statement, "ss", $username, $password);     mysqli_stmt_execute($statement);      mysqli_stmt_store_result($statement);     mysqli_stmt_bind_result($statement, $userid, $name, $age, $username, $password);      $user = array();      while(mysqli_stmt_fetch($statement)){     $user[name] = $name;     $user[age] = $age;     $user[username] = $username;     $user[password] = $password;     }      echo json_encode($user);     mysqli_stmt_close($statement);       mysqli_close(mysqli);  ?> 

either database user or password wrong(or both). check again if user exists database on host.

also check case of characters.