Mysql - Help me alter this search query to get desired results

Question

Following is a dump of the tables and data needed to answer understand the system:-

The system consists of tutors and classes. The data in the table

Answer 1

I think this query would help you:

SET @tag1 = 1, @tag2 = 4; -- Setting some user variables to see where the ids go. (you can put the values in the query)

SELECT wtagrels.id_wc,
  SUM(DISTINCT( wtagrels.id_tag =@tag1 OR wtagrels.id_tutor =@tag1)) AS key_1_total_matches,
  SUM(DISTINCT( wtagrels.id_tag =@tag2 OR wtagrels.id_tutor =@tag2)) AS key_2_total_matches
FROM   all_tag_relations AS wtagrels
WHERE  ( wtagrels.id_tag =@tag1 OR wtagrels.id_tag =@tag2 )
GROUP  BY wtagrels.id_wc
HAVING key_1_total_matches = 1 AND key_2_total_matches = 1
LIMIT  0, 20

It returns id_wc = 1.
For (6, 3) the query returns nothing.