Why do the inserted values ​​need to be concatenated?

Question

values('" . $username . "','" . $password . "','" . $time . "','" . $ip . "')";

values ("$username","$password","$time","$ip")Isn't this possible?

Answer 1

Because you need to correspond to the data type of each field in the database, if the string is not enclosed in quotation marks, an error will be reported