Mysql + GMAPs - 从DB中选择并计算距离

Question

I have MySQL table with some libraries. I need to make SQL query in PHP, which will select library by ID, and count distance. This is invalid query. Where I'm doing mistake in this query ?

$query = "SELECT *,  
    ( 6371 * 
        acos(
            cos(radians(" . $center_lat . ")) *
            cos(radians(lat)) *
            cos(radians(lng) - radians(" . $center_lng . ")) +
            sin(radians(" . $center_lat . ") ) *
            sin(radians( lat ) )
        )
    ) AS distance
FROM `libraries`
WHERE id = ". $id ."
LIMIT 0 , 1";