Performing math operation on temporary column in SQL

Question

What I\'m trying to do is have it where I get the occurances on an id in the table, and then based upon the amount of occurances, divide the value of another column by that valu

Answer 1

Just throw it in a sub-query and do the math after that:

SELECT t_id, occurances, value/occurances AS newValue
from (
    SELECT t.t_id, count(DISTINCT tm.tm_id) AS occurances, t.value
    FROM table t
    INNER JOIN table_map tm ON t.t_id = tm.tm_id
    GROUP BY t.t_id
    HAVING occurances > 1) t

Answer 2

Maybe you meant something like this:

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