DROP TABLE IF EXISTS test.agg_over_nullable;
CREATE TABLE test.agg_over_nullable (
	partition Date,
	timestamp DateTime,
	user_id Nullable(UInt32),
	description Nullable(String)
) ENGINE = MergeTree(partition, timestamp, 8192);

INSERT INTO test.agg_over_nullable(partition, timestamp, user_id, description) VALUES(now(), now(), 1, 'ss');
INSERT INTO test.agg_over_nullable(partition, timestamp, user_id, description) VALUES(now(), now(), 1, NULL);
INSERT INTO test.agg_over_nullable(partition, timestamp, user_id, description) VALUES(now(), now(), 1, 'aa');

SELECT groupUniqArray(description) FROM test.agg_over_nullable;
SELECT topK(3)(description) FROM test.agg_over_nullable;

DROP TABLE test.agg_over_nullable;