PHP and MySQL query - multiple criteria - php

Question

I'm having a problem with the code listed below where I'm running a query on a database based on search criteria the user may have selected on a form.
At the moment, querying the database just on the author's name works fine. But if I uncomment the rest of the if-else statements, none of the queries work. I just get a blank table back with no results returned.
I've tried each if/else statement individually with the others commented out and they all work fine on their own, but not when they're all uncommented.
Can anyone point me in the right direction?
$query = "SELECT * FROM books WHERE book_no IS NOT NULL";
if ($_POST['author'])
$query .= " AND '$author' = author";
/*
else if ($_POST['author'] AND $_POST['year'])
$query .= " AND '$author' = author AND '$year' = year";
*/
/*
else if ($_POST['cover_art']) {
$query .= " AND '$cover_art' = cover_art";
}
*/
/*
else if ($_POST['interior_art']) {
$query .= " AND '$cover_art' = cover_art";
}
else {
// do something else
}
*/

Answer 1

Check this solution:
$author='Bred';
$year='2012';
$cover_art='';
$queryA=array();
if ($author<>'') $queryA []= "'$author' = author";
if ($year<>'') $queryA []= "'$year' = year";
if ($cover_art<>'') $queryA []= "'$cover_art' = cover_art";
$query = "SELECT * FROM books WHERE book_no IS NOT NULL";
if(count($queryA)>0) $query.=' AND '.implode(' AND ',$queryA);
echo $query;