DROP TABLE IF EXISTS rollup_having;
CREATE TABLE rollup_having (
  a Nullable(String),
  b Nullable(String)
) ENGINE = Memory;

INSERT INTO rollup_having VALUES (NULL, NULL);
INSERT INTO rollup_having VALUES ('a', NULL);
INSERT INTO rollup_having VALUES ('a', 'b');

SELECT a, b, count(*) FROM rollup_having GROUP BY a, b WITH ROLLUP HAVING a IS NOT NULL;
SELECT a, b, count(*) FROM rollup_having GROUP BY a, b WITH ROLLUP HAVING a IS NOT NULL and b IS NOT NULL;

DROP TABLE rollup_having;