Talvez você quis dizer algo assim:
SELECT
t.t_id,
t.occurrences,
t.value / tm.occurrences AS newValue
FROM table t
INNER JOIN (
SELECT
tm_id,
COUNT(*) AS occurrences
FROM table_map
GROUP BY tm_id
HAVING COUNT(*) > 1
) tm ON t.t_id = tm.tm_id
