set hive.fetch.task.conversion=more;

DESCRIBE FUNCTION concat;
DESCRIBE FUNCTION EXTENDED concat;

SELECT
  concat('a', 'b'),
  concat('a', 'b', 'c'),
  concat('a', null, 'c'),
  concat(null),
  concat('a'),
  concat(null, 1, 2),
  concat(1, 2, 3, 'a'),
  concat(1, 2),
  concat(1),
  concat('1234', 'abc', 'extra argument')
FROM src tablesample (1 rows);

-- binary/mixed
SELECT
  concat(cast('ab' as binary), cast('cd' as binary)),
  concat('ab', cast('cd' as binary))
FROM src tablesample (1 rows);