Database Queries

Hi Guys,

I am currently working on building a function using global $wpdb to select some values to add into a hook using add_filter. Is it acceptable to run a database call more than once in a function? I am more thinking on Security issues. The code I am starting with is :-

global $wpdb;

$postinfo = $wpdb->get_results( "SELECT * FROM ls_posts WHERE ID = '$postid'", OBJECT );
$postimage = $wpdb->get_results( "SELECT * FROM ls_posts WHERE post_parent = '$postid'", OBJECT );

Any information would be greatly appreciated
Many Thanks
J