$sth->prepare("SELECT * FROM companies WHERE name = '$name'");

##</code><code>##

  $sth->prepare("SELECT * FROM companies WHERE name = ?");

##</code><code>##

  $sth->prepare("SELECT name, url FROM table WHERE name LIKE '$name%');

##</code><code>##

  $sth->prepare("SELECT name, url FROM table WHERE name LIKE ?");
  $sth->execute($name . '%');