The difference between bindParam() and bindValue()

bettermysql-bindParam.php

<?php
  // Assuming that database connection is already open
  // Get username
  $username = 'johndoe';
  
  $stmt = $db->prepare("SELECT user, email, country FROM users WHERE user = :username");
  $stmt->bindParam(':username', $username);
  $username = 'janesmith';
  
  $stmt->execute();
  // Statement will be executed using 'janesmith' as the username...
  // because :username searches for $username upon execution, and
  // the last known value of $username is 'janesmith'
?>

bettermysql-bindValue.php

<?php
  // Assuming that database connection is already open
  // Get username
  $username = 'johndoe';
  
  $stmt = $db->prepare("SELECT user, email, country FROM users WHERE user = :username");
  $stmt->bindValue(':username', $username);
  $username = 'janesmith';
  
  $stmt->execute();
  // Statement will be executed using 'johnsmith' as the username...
  // because the literal value "johndoe" has been bound to :username
  // prior to the bindValue() function. Further changes to $username
  // will not be reflected in the prepared statement.
?>

you have a mistake the second example should be johndoe not johnsmith.

 $stmt->bindValue(':username', $username);
  $username = 'janesmith';
  
  $stmt->execute();
  // Statement will be executed using 'johndoe' as the username...