Who knows how to fix?

Warning: Invalid argument supplied for foreach() in C:\OSPanel\domains\web\DB\db.php on line 30

Вот код:

1. <?php
2. $dbhost = "localhost";
3. $dbname = "test_saneto";
4. $username = "root";
5. $password = "";
6. $db = new PDO("mysql:host=$dbhost; dbname=$dbname", $username, $password);
7. // Получение всех статей
8. function get_singles_all(){
9. global $db;
10. $singles = $db->query("SELECT * FROM singles ORDER BY id DESC");
11. return $singles;
12. }
13. // Получение статьи по ее id
14. function get_single_by_id($id){
15. global $db;
16. $singles = $db->query("SELECT * FROM singles WHERE id = $id");
17. foreach($singles as $single){
18. return $single;
19. }
20. }
21. // Получение названия категории
22. function get_category_by_id($id){
23. global $db;
24. $categories = $db->query("SELECT * FROM categories WHERE id = $id");
25. foreach($categories as $category){
26. return $category["category_id"];
27. }
28. }
29. // Получение имен авторов
30. function get_authors_by_id($id){
31. global $db;
32. $authors = $db->query("SELECT * FROM authors WHERE id = $id");
33. foreach($authors as $author){
34. return $author["author_name"];
35. }
36. }
37. // Получение комментариев
38. function get_comments_all(){
39. global $db;
40. $comments = $db->query("SELECT * FROM comments");
41. return $comments;
42. }
43. // Получение комментариев по id
44. function get_comments_all_by_id($id){
45. global $db;
46. $comments = $db->query("SELECT * FROM comments WHERE id_comment = $id");
47. foreach($comments as $comment){
48. return $comment["comment_text"];
49. }
50. }