postgresql – Postgres not returning data on array_agg query as below

The problem arise when there are no data for books in specific library. Consider a following working scenario.

Table name: library

--------------------------------
| id |    name     |    owner  |
--------------------------------
|  1 |     ABC     |     A     |
|  2 |     DEF     |     D     |
|  3 |     GHI     |     G     |
--------------------------------

Table name: books

--------------------------------
| id |    title    |  library  |
--------------------------------
|  a |     xxx     |     1     |
|  b |     yyy     |     1     |
|  c |     zzz     |     2     |
--------------------------------

Now when I do query like below:

SELECT library.name, array_agg(b.title) AS book_list FROM library, 
(SELECT title FROM books WHERE books.library = :library_no) as b 
WHERE library.id = :library_no GROUP BY library.id

The query generates output for library 1 & 2, but not for library 3. Why and how to solve this issue? (Generate an empty list on no library books)

PS: I’ve even tried coalesce as below:

SELECT library.name, coalesce(array_agg(b.title), ARRAY()::VARCHAR()) AS book_list FROM library, 
(SELECT title FROM books WHERE books.library = :library_no) as b 
WHERE library.id = :library_no GROUP BY library.id