adding the word NO – simple

my page uploads all of the forms data into the database, however when it does this i also want it to upload the word NO into a field called valid in each record. What is the correct syntax

$firstname = $_POST[‘firstname’];
$lastname = $_POST[‘lastname’];
$username = $_POST[‘username’];
$password = $_POST[‘password’];

BUT WHAT DO I PUT AFTER THOSE TO ADD ‘NO’ TO ALL THE valid FIELDS

i’ve tried

$valid = ‘NO’;

but it doesn’t work

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