MySQL: Select MAX() from sub-query with COUNT()

Question

Before you mark this as duplicate please take a look at this SQLFiddle.

I have this schema:

CREATE TABLE book(book_id int,
                   book_name varchar(100),
                   author_id int,
                   editor_id varchar(100),
                   isbn varchar(100));
INSERT INTO book
VALUES
(1 , 'Book1 Title' ,  12  ,  'Editor1'   , '8000-9000' ),
(2 , 'Book2 Title' ,  98  ,  'Editor1'   , '8000-9001' ),
(1 , 'Book1 Title' ,  12  ,  'Editor1'   , '8000-9002' ),
(3 , 'Book3 Title' ,  3  ,  'Editor1'   , '8000-9003' );

CREATE TABLE author(author_id int,
                    fn varchar(100),
                    ln varchar(100));
INSERT INTO author
VALUES
(12, 'name1','lname1'),
(98,'name2','lname2'),
(3,'name3','lname3');

The sub-query:

  SELECT c.author_id,COUNT(*) book_count FROM book c
  GROUP BY c.author_id

has a result:

| AUTHOR_ID | BOOK_COUNT |
--------------------------
|         3 |          1 |
|        12 |          2 |
|        98 |          1 |

Now, the tricky part here is the result of this query:

SELECT MAX(book_count),a.* FROM
author a,(
  SELECT c.author_id,COUNT(*) book_count FROM book c
  GROUP BY c.author_id
) b 
where a.author_id = b.author_id

is this:

| MAX(BOOK_COUNT) | AUTHOR_ID |    FN |     LN |
------------------------------------------------
|               2 |         3 | name3 | lname3 |

which should be like this:

| MAX(BOOK_COUNT) | AUTHOR_ID |    FN |     LN |
------------------------------------------------
|               2 |        12 | name1 | lname1 |

What do you think is wrong in the query?

Solution 1

Instead of MAX() you can simply use LIMIT for the same. Also use JOIN instead.

SELECT book_count,a.author_id,a.fn, a.ln 
FROM author a
JOIN
(
  SELECT c.author_id,COUNT(*) book_count FROM book c
  GROUP BY c.author_id
) b 
ON a.author_id = b.author_id
ORDER BY book_count DESC LIMIT 1

Output:

| BOOK_COUNT | AUTHOR_ID |    FN |     LN |
-------------------------------------------
|          2 |        12 | name1 | lname1 |

See this SQLFiddle

---

Edit:

If you want to use MAX() for that, you have to use sub-query like this:

SELECT book_count,a.author_id,a.fn, a.ln 
FROM author a
JOIN
(
  SELECT c.author_id,COUNT(*) book_count FROM book c
  GROUP BY c.author_id
) b 
ON a.author_id = b.author_id
WHERE book_count = 
        (SELECT MAX(book_count)
        FROM
        (
           SELECT c.author_id,COUNT(*) book_count FROM book c 
           GROUP BY c.author_id
        ) b )

See this SQLFiddle

---

Edit2:

Instead of using LIMIT in outer query you can simply use it in inner query too:

SELECT book_count,a.author_id,a.fn, a.ln 
FROM author a
JOIN
(
  SELECT c.author_id,COUNT(*) book_count FROM book c
  GROUP BY c.author_id
  ORDER BY COUNT(*) DESC LIMIT 1
) b 
ON a.author_id = b.author_id

See this SQLFiddle

Solution 2

In fact, MySQL has a lack of support SQL's standard, because it allows use aggregate functions w/o GROUP BY clause and returns random data in result. You should avoid the usage of aggregates in that way.

EDIT: I mean, for example in MySQL you can execute query like this:

SELECT
  MAX(a), b, c
FROM
  table
GROUP BY
  b;

Which returns random data in c column, and that's terribly wrong.