Question: I am doing a library management system project.
I am staff at mysql query.

I have books table (books), in that fields are `book_id | book_name | isbn_no| publisher_info` 

I have another table of reader (reader) in this `reader_id | book_id | reader_name | reader_info | and book_return_status`

Now I want the result of book list which are not in reader table, so that list will become an available book list. 

```
select * from books,reader where books.book_id != reader.book_id and reader.book_return_status = 1 

```

But not gives me proper result, I have also tried out this one query..

```
 select * from books where book_id not in (select * from reader where book_return_status = 1)

```

But I haven't given my result.

I want to book list which are not in reader table.

Answer: 
You are close with your second query. However, for `not in` to work, your sub-query must return only ids:

```
 select * from books where book_id not in (select book_id from reader where book_return_status = 1)

```
Try this query 

```
select * from books where book_id not in (select reader_id from reader where book_return_status = 1)

```