PHP AND OR，这有效吗？

Is this valid? I want to check if 'One' is not blank AND two is either blank or undefined. Can i use the brackets that way around both of GET[two]?

if( $_GET["one"] == '' &&  ($_GET["two"] == '' ||  $_GET["two"] == 'undefined') ) {
 // do X
}

Thanks

Yes, it's certainly valid. Basically, your if checks if BOTH cases (1) one == '' and (2) two == '' or two == 'undefined' exists. (2) evaluates as true if two is either '' or 'undefined'

The brackets are perfectly valid. :)

Yes, that is valid. It should do exactly what you want.

If you need to check for empty strings or NULL values, you can also use the empty() function:

if (empty($_GET['one']))