Funso (Chichewa): Ndi boma liti lomwe linalemba mitengo ya chimanga pa tsiku limodzi lokha?
Question (English): Which district recorded maize prices only on a single collection date?
Table: commodity_prices (difficulty: hard)
SQL: SELECT district FROM commodity_prices WHERE commodity = 'Maize' GROUP BY district HAVING COUNT(DISTINCT collection_date) = 1;
Result: [('Zomba',)]