PostgreSQL query for Library Management System - sql

Question

Get the member ID and name of the members to whom no more books can be issued, because they have already got as many books issued as the number for which they are entitled
Following are the schemas:
Book_Records(accession_no,isbn_no)
Book(isbn_no, author, publisher, price)
Members(member_id, member_name,max_no_books,max_no_days)
Book_Issue(member_id,accession_no,issue_date,return_date)
CREATE TABLE BOOK (ISBN_NO VARCHAR(35) PRIMARY KEY,
AUTHOR VARCHAR(35) NOT NULL,
PUBLISHER VARCHAR(35) NOT NULL,
PRICE NUMERIC(10,3));
CREATE TABLE BOOK_RECORDS(ACCESSION_NO VARCHAR(35) PRIMARY KEY,
ISBN_NO VARCHAR(35) REFERENCES BOOK(ISBN_NO));
CREATE TABLE MEMBERS(MEMBER_ID VARCHAR(35) PRIMARY KEY,
MEMBER_NAME VARCHAR(35) NOT NULL,
MAX_NO_BOOKS INT,
MAX_NO_DAYS INT);
CREATE TABLE BOOK_ISSUE(MEMBER_ID VARCHAR(35) REFERENCES MEMBERS(MEMBER_ID),
ACCESSION_NO VARCHAR(35) REFERENCES
BOOK_RECORDS(ACCESSION_NO),
ISSUE_DATE DATE NOT NULL,
RETURN_DATE DATE,
PRIMARY KEY(MEMBER_ID,ACCESSION_NO));
I tried the following query but fails.
SELECT DISTINCT member_name
FROM members AS m
JOIN (
SELECT member_id, COUNT(*) AS no_books_issued
FROM book_issue
GROUP BY member_id,accesion_no
HAVING no_books_issued >= max_no_books
) AS b ON m.member_id = b.member_id;

Answer 1

Presumably, a query like this gets the number of books currently issued:
SELECT member_id, COUNT(*) AS num_books
FROM book_issue
WHERE return_date IS NULL
GROUP BY member_id;
My understanding of the maximum number of books would be concurrently -- that is, only count books that have not been returned. Perhaps you have a different definition.
Then, you can use this in a JOIN, doing the comparison on the maximum outside the subquery:
SELECT member_name
FROM members m JOIN
(SELECT member_id, COUNT(*) AS num_books
FROM book_issue
WHERE return_date IS NULL
GROUP BY member_id
) b
ON b.member_id = m.member_id AND
b.num_books >= m.max_no_books;
Notes:
In a JOIN, the comparison to the outer table needs to be outside the subqueries.
No SELECT DISTINCT is needed.
The GROUP BY for counting books should be only at the member level.