Problem with a complex query
Do you mean exactly one occurrence?  Or at least one occurrence?

These will (I think) find No for "at least":

SELECT No  FROM tbl AS m
WHERE  EXISTS ( SELECT 1 FROM tbl WHERE
                 No = m.No AND  letter IN ('a', 'x', 'y', 'z') )
  AND  EXISTS ( SELECT 1 FROM tbl WHERE
                 No = m.No AND  letter IN ('b', 'w', 'l') )
  AND  EXISTS ( SELECT 1 FROM tbl WHERE
                 No = m.No AND  letter IN ('c', 'k', 'j') )


Another...

SELECT No
    FROM ( SELECT No, GROUP_CONCAT(letter SEPARATOR '') AS lets
               FROM table
               GROUP BY No
               HAVING lets RLIKE '[axyz]'
                  AND lets RLIKE '[bwl]'
                  AND lets RLIKE '[ckj]' ) AS n


(Nothing even close to your invented IN syntax is allowed.)