Two-part conditional sql statement

Question

The statement below is querying a log table and I'm trying to get the max budget depending on the scenario if falls within.

Error message:

Expressions referencing the outer query are not supported outside of WHERE/HAVING clause

SELECT
    id, status, budget,
    CASE 
        WHEN (status == 'RUNNING' AND status == 'NOT RUNNING') 
            THEN (SELECT MAX(budget) 
                  FROM status_table 
                  WHERE status == 'RUNNING')
        WHEN (status == 'RUNNING') 
            THEN (SELECT MAX(budget) 
                  FROM status_table 
                  WHERE status == 'RUNNING')
        WHEN (status == 'NOT RUNNING') 
            THEN (SELECT MAX(budget) 
                  FROM status_table 
                  WHERE status == 'NOT RUNNING')
        ELSE MAX(budget)
    END AS max_budget
FROM 
    status_table 
GROUP BY
    id, status, budget

Answer 1

Seems to me you want to find the row(s) with the maximum budget where the status is either RUNNING or NOT RUNNING.

SELECT id
      ,status
      ,budget
  FROM status_table
 WHERE budget = (
                  SELECT max(budget)
                    FROM (
                           SELECT max(budget)
                             FROM status_table
                            WHERE status = 'RUNNING'
                           UNION
                           SELECT max(budget)
                             FROM status_table
                            WHERE status = 'NOT RUNNING'
                         )
                )