This function worked for me:
function get_complete_meta( $post_id, $meta_key ) {
global $wpdb;
$mid = $wpdb->get_results( $wpdb->prepare("SELECT * FROM $wpdb->postmeta WHERE post_id = %d AND meta_key = %s", $post_id, $meta_key) );
if( $mid != '' )
return $mid;
return false;
}
it will return an array of objects like:
Array
(
[0] => stdClass Object
(
[meta_id] => 1002
[post_id] => 1
[meta_key] => my_key
[meta_value] => my_value
)
[1] => stdClass Object
(
[meta_id] => 1003
[post_id] => 668
[meta_key] => my_key
[meta_value] => another value
)
)