Building WHERE clauses from multiple $_GET's - php

Question

I am currently trying to write complex MySQL WHERE clauses that are generated from $_GET variables (which themselves come from select dropdowns). First, a bit of code so you know what I am talking about:
if(!isset($_GET['order'])){
$order= 'start asc';
} elseif ($_GET['order'] == "dateasc") {
$order= 'start asc';
} elseif ($_GET['order'] == "titleasc") {
$order= 'title asc';
} elseif ($_GET['order'] == "titledesc") {
$order= 'title desc';
};
if(!isset($_GET['cat'])){
$cat= '0';
} else {
$cat = $_GET['cat'];
};
if(!isset($_GET['loc'])){
$loc= '0';
} else {
$loc = $_GET['loc'];
};
if (isset($_GET['sd']) || isset($_GET['ed']) || isset($_GET['cat']) || isset($_GET['loc']) || isset($_GET['order']) ) {
$where = 'WHERE ';
if (isset($_GET['sd'])) {
$where .= "start = " . $_GET['sd'];
};
if (isset($_GET['ed'])) {
$where .= "AND end = " . $_GET['ed'];
};
if (isset($_GET['cat'])) {
$where .= "AND category = " . $_GET['cat'];
};
if (isset($_GET['loc'])) {
$where .= "AND location = " . $_GET['loc'];
};
};
$result = mysql_query("SELECT * FROM " . TABLE . $where . " ORDER BY " . $order);
Obviously this isn't working, otherwise I wouldn't be here. :) Basically, I have 4 variables that I want to conditionally use for sorting in my query: start date, and end date, a category, and a location. My problem is that all 4 of these may not always be used.. so given the above example, there might be a case where someone selects a category ($cat) but NOT a start date ($sd)... which means my WHERE clause would start off with 'AND', which is obviously invalid. So how do I build a query based off variables that may or may not be used?
I really feel like I am overthinking this, and I am afraid of writing 9000 lines of isset tests to account for every combination of $_GET variable usage. Surely there a simple way to build a WHERE clause from multiple $_GETs that may or may not be used every time..? I've tried Googling but can only find solutions that suggest using a framework for building complex queries and that just seems overly... clunky... for such a simple problem.

Answer 1

If you're just worried about having a where clause that starts with AND you can add 1=1 to account for no filters.
WHERE 1=1
Then, if you have any filters, it will look like this:
WHERE 1=1 AND col1=? AND col2=?

Answer 2

This may not be the cleanest solution, but it should be fairly simple to understand and implement.
if (isset($_GET['sd']) || isset($_GET['ed']) || isset($_GET['cat']) || isset($_GET['loc']) || isset($_GET['order']) ) {
$where = 'WHERE ';
if (isset($_GET['sd'])) {
if(strlen($where) > 6) {
$where .= " AND ";
}
$where .= "start = " . $_GET['sd'];
}
if (isset($_GET['ed'])) {
if(strlen($where) > 6) {
$where .= " AND ";
}
$where .= "end = " . $_GET['ed'];
}
if (isset($_GET['cat'])) {
if(strlen($where) > 6) {
$where .= " AND ";
}
$where .= "category = " . $_GET['cat'];
}
if (isset($_GET['loc'])) {
if(strlen($where) > 6) {
$where .= " AND ";
}
$where .= "location = " . $_GET['loc'];
}
}