当测试张贴的表单值是否包含等于XX php的文本时，正确的语法是什么?

what is the correct syntax to use when testing if a posted form value contains text equal to XX php

 $field = $_POST['myfield'];
 if($field == 'Hello world') {
 / /do something 
 }

$field =(isset($_POST['myfield']))?$_POST['myfield']:'';
    if($field == 'Hello world') {
     / /do something 
     }