email_address   | brand | region | area | site | lowest_distinct_level
----------------|-------|--------|------|------|----------------------
alpha@gmail.com |   1   |    1   |   1  |   2  |
beta@gmail.com  |   1   |    1   |   2  |   0  |
gamma@gmail.com |   1   |    1   |   2  |   2  |
zeta@gmail.com  |   1   |    2   |   0  |   0  |

select email_address, brand, region, area, site,
    case when site = 1 then 'site'
         else case when area = 1 then 'area'
              else case when region = 1 then 'region'
                   else case when brand = 1 then 'brand'
                             else ''
                             end
                   end
              end
         end
from mm;

+-----------------+-------+--------+------+------+--------+
| email_address   | brand | region | area | site |  case  |
+-----------------+-------+--------+------+------+--------+
| alpha@gmail.com | 1     | 1      | 1    | 2    |  area  |
+-----------------+-------+--------+------+------+--------+
| beta@gmail.com  | 1     | 1      | 2    | 0    | region |
+-----------------+-------+--------+------+------+--------+
| gamma@gmail.com | 1     | 1      | 2    | 2    | region |
+-----------------+-------+--------+------+------+--------+
| zeta@gmail.com  | 1     | 2      | 0    | 0    |  brand |
+-----------------+-------+--------+------+------+--------+