Mapping a column between two tables

Anonymous OK, so I would think you would first need to modify your calculated table to this:

UniqueCombinationSummary = 
ADDCOLUMNS(
  SUMMARIZE( 'SQL_Database_Website',
    'SQL_Database_Website'[Department],
    'SQL_Database_Website'[City],
    'SQL_Database_Website'[Country],
    'SQL_Database_Website'[Division],
    "UniqueDivisionCount", DISTINCTCOUNT('SQL_Database_Website'[Division]) ),
  "Key", [Department] & "|" & [City] & "|" & [Country] & "|" & [Division]
)

Then in your other table, a calculated column like this:

Division = 
  VAR __Department = [Department]
  VAR __City = [City]
  VAR __Country = [Country]
  VAr __Result = 
    MAXX(
      FILTER(
        'UniqueCombinationSummary',
        [UniqueDivisionCount] = 1,
        [Department] = __Department,
        [City] = [City],
        [Country] = __Country
      ),
      [Division]
    )
RETURN
  __Result

And then another calculated column in that table:

Key = [Department] & "|" & [City] & "|" & [Country] & "|" [Division]

Then relate your tables on the Key columns.