user: Question: Which band serves Darwin for Commercial purpose?
Columns: ['Callsign', 'Area served', 'Frequency', 'Band', 'Freq currently', 'Purpose']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['5AL', 'Alice Springs', '1530', 'AM', '8AL (783 kHz)', 'National']
SQL:

assistant: SELECT "Band" FROM "Table" WHERE "Area served" = 'Darwin' AND "Purpose" = 'Commercial';