Where clause, with if statement

Hi everyone, this is the first time that I've done much with PHP
My question is how would I include an IF statement within a WHERE clause, so that I can ignore the item if its submitted value is null? $datemonthF and $datedayF are the submitted values.
Here's what I have now:
$query .= "WHERE datemonth = '". $datemonthF ."' and dateday = '". $datedayF ."'";
I'd like to negate each one that has the value null. I could also make it so they are negated if the value is nothing, "", whichever is easier. Thanks for any help!

Hi everyone, this is the first time that I've done much with PHP
My question is how would I include an IF statement within a WHERE clause, so that I can ignore the item if its submitted value is null? $datemonthF and $datedayF are the submitted values.
Here's what I have now:
$query .= "WHERE datemonth = '". $datemonthF ."' and dateday = '". $datedayF ."'";
I'd like to negate each one that has the value null. I could also make it so they are negated if the value is nothing, "", whichever is easier. Thanks for any help!

$c1 = isset($datemonthF) && !empty($datemonthF);
$c2 = isset($datedayF) && !empty($datedayF);
if($c1 || $c2){
$query .= "WHERE";
if($c1){
$query .= " datemonth = '". $datemonthF ."'";
}
if($c1 && $c2){
$query .= " and ";
}
if($c2){
$query .= " dateday = '". $datedayF ."'";
}
}


best regards

perfect! thanks for the help!