Mysql - Ayúdame a modificar esta consulta de búsqueda para obtener los resultados deseados

Creo que esta consulta te ayudaría:

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 [email protected] OR wtagrels.id_tutor [email protected])) AS key_1_total_matches,
  SUM(DISTINCT( wtagrels.id_tag [email protected] OR wtagrels.id_tutor [email protected])) AS key_2_total_matches
FROM   all_tag_relations AS wtagrels
WHERE  ( wtagrels.id_tag [email protected] OR wtagrels.id_tag [email protected] )
GROUP  BY wtagrels.id_wc
HAVING key_1_total_matches = 1 AND key_2_total_matches = 1
LIMIT  0, 20

Devuelve id_wc = 1 .
Para (6, 3) la consulta no devuelve nada.