SQL query to find all retailers within a given radius of a Latitude and Longitude

function retailerSearch($latitude, $longitude, $radius){
	$latitude = (int)$latitude;
	$longitude = (int)$longitude;
	$radius = (int)$radius;
	$degree = '69.17032342863616';
 
	$dpmLAT = (1 / $degree);
	$radiusLAT = ($dpmLAT * $radius);
	$minLAT = ($latitude - $radiusLAT); 
	$maxLAT = ($latitude + $radiusLAT);
 
	$mpdLNG = ($degree * cos($latitude * (pi / 180)));
	$dpmLNG = (1 / $mpdLNG);
	$radiusLNG = ($dpmLNG * $radius);
	$minLNG = ($longitude - $radiusLNG);
	$maxLNG = ($longitude + $radiusLNG);
 
	$subQuery = "
		SELECT
			`retail_id`
		FROM
			`retail_locations`
		WHERE
			`latitude` BETWEEN {$minLAT} AND {$maxLAT}
			AND
			`longitude` BETWEEN {$minLNG} AND {$maxLNG}
	";
 
	$query = "
		SELECT 
			* 
		FROM
			`retail_items` 
		WHERE
			`id` = (
				{$subQuery}
			)
	";
 
	echo $query;
 
}