SELECT *
FROM xrollup

Query id: e702f6fe-8595-4a9f-aeff-ea65e2045801

┌─metric─┬──────────b─┬─v─┐
│      2 │ 2018-01-01 │ 1 │
│      2 │ 2018-02-02 │ 1 │
└────────┴────────────┴───┘
┌─metric─┬──────────b─┬─v─┐
│      1 │ 2018-01-01 │ 1 │
│      1 │ 2018-01-02 │ 1 │
│      1 │ 2018-02-01 │ 1 │
│      1 │ 2017-03-01 │ 1 │
└────────┴────────────┴───┘

6 rows in set. Elapsed: 0.004 sec.

SELECT
    b,
    sum(v)
FROM xrollup
GROUP BY b
    WITH TOTALS
ORDER BY b DESC WITH FILL
LIMIT 5

Query id: ae21086d-eb89-4b73-b9be-7baa4c0cee27

┌──────────b─┬─sum(v)─┐
│ 2018-02-02 │      1 │
│ 2018-02-01 │      1 │
│ 2018-01-31 │      0 │
│ 2018-01-30 │      0 │
│ 2018-01-29 │      0 │
└────────────┴────────┘

Totals:
┌──────────b─┬─sum(v)─┐
│ 1970-01-01 │      6 │
└────────────┴────────┘

5 rows in set. Elapsed: 0.003 sec.

SELECT
    b,
    sum(v)
FROM xrollup
GROUP BY b
    WITH TOTALS
ORDER BY b DESC WITH FILL FROM today()
LIMIT 5

Query id: cbf3d659-cf10-4b3b-800f-a5af11fc9faa

┌──────────b─┬─sum(v)─┐
│ 2021-02-18 │      0 │
│ 2021-02-17 │      0 │
│ 2021-02-16 │      0 │
│ 2021-02-15 │      0 │
│ 2021-02-14 │      0 │
└────────────┴────────┘

Totals:
┌──────────b─┬─sum(v)─┐
│ 2021-02-18 │      0 │
└────────────┴────────┘

5 rows in set. Elapsed: 0.006 sec.