mysql - Unexpected T_CONSTANT_ENCAPSED_STRING error in SQL Query

I am getting an unexpected T_CONSTANT_ENCAPSED_STRING error in the following SQL query:

mysql_query (UPDATE 'wp_posts' SET 'post_status' = 'publish' WHERE 'post_id' = '$id');

Can you guys see where the error might be?

Here is the full code in case it helps:

    $key = 'feed';
    $post_ids = array(2263, 2249); 


    foreach ($post_ids as $id) {
    $feedurl = get_post_custom_values($key, $id);
    $feedurlstr = implode($feedurl);

    // Ignore - it determines whether feed is live and returns $result
    LiveOrNot($feedurlstr);

    if ( $result == "live" ) {
    mysql_query (UPDATE 'wp_posts' SET 'post_status' = 'publish' WHERE 'post_id' = '$id');

    }    
    elseif ( $result == "notlive" ) {
    mysql_query (UPDATE 'wp_posts' SET 'post_status' = 'draft' WHERE 'post_id' = '$id');
    }
    endif;
    }

Answer

Wrap your SQL statements in quote-marks - ".

mysql_query ("UPDATE 'wp_posts' SET 'post_status' = 'publish' WHERE 'post_id' = '$id'");