MySQL: Select distinct values from one column if other column has two determined values in junction table

Question

I have junction table:

CREATE TABLE `book_tags` (
  `id` int(11) NOT NULL,
  `book_id` int(11) DEFAULT NULL,
  `tag_id` int(11) DEFAULT NULL
) ENGINE=MyISAM DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;

with values like

INSERT INTO `book_tags` (`id`, `book_id`, `tag_id`) VALUES
(3, 20, 1),
(4, 20, 2),
(5, 21, 1),
(6, 22, 2),
(7, 24, 2);

How can I find the books (book_id) which have two or more determined tags at the same time? For example, how can I find a book which have tag_id=2 AND tag_id=1

+++++++++++++++++++++++++++++++++++++++

UPDATED :

Looking through stackoverflow I've found the answer on my question.

For 2 required tags the solution will be:

SELECT * FROM `book_tags`
WHERE `tag_id` IN (1, 2)
GROUP BY book_id 
HAVING COUNT(*) = 2

This solution is suitable for my particular case, since I know that in my table there is no rows with the same pair of values of book_id and tag_id.

Thank you @Barbaros Özhan and @scaisEdge for help!

Answer 1

You could try using a subquery for tag_id in you searched set and the check for count distinct tag_id quae to the number of your searched tag

Assuming tag 1, 2 then

select book_id 
from (
  select book_id, tag_id 
  from  book_tags 
  where tag_id in  (1,2)
) t 
group by book_id
having count(distinct tag_id) = 2  


select book_id 
from (
  select book_id, tag_id 
  from  book_tags 
  where tag_id in  (1,2,5,7, 9, 11)
) t 
group by book_id
having count(distinct tag_id) = 5  

Answer 2

It would be an elastic option using a having clause as in the following way as you add after in operator's list( in (1,2,3,...) ) more tag_id to filter:

select `book_id` 
  from `book_tags` 
 where `tag_id` in (1,2,3) 
 group by `book_id` 
having count(`tag_id`) = count(distinct `tag_id`)
   and count(distinct `tag_id`) > count(distinct `book_id`);

Demo

Answer 3

SELECT book_id FROM books_tags WHERE tag_id = 1 OR tag_id = 2 ?

Or

SELECT book_id FROM books_tags WHERE tag_id IN (1, 2)