データベースから毎日ログインしているユーザー名を取得する

DECLARE @from_date DATETIME, @to_date DATETIME

-- populate @from_date and @to_date based on reporting needs
-- possibly using MIN() and MAX() on your logged_in and logged_out fields

DECLARE
  @limit INT
SELECT
  @limit = DATEDIFF(DAY, @from_date, @to_date)
;
WITH
  calendar AS
(
  SELECT DATEADD(DAY, DATEDIFF(DAY, 0, @from_date), 0) AS date, 1 AS inc_a, 2 AS inc_b
UNION ALL
  SELECT DATEADD(DAY, DATEDIFF(DAY, 0, @from_date) + inc_a, 0), inc_a + inc_a + 1, inc_a + inc_a + 2 FROM calendar WHERE inc_a <= @limit
UNION ALL
  SELECT DATEADD(DAY, DATEDIFF(DAY, 0, @from_date) + inc_b, 0), inc_b + inc_b + 1, inc_b + inc_b + 2 FROM calendar WHERE inc_b <= @limit
)

SELECT
  calendar.date,
  your_table.username
FROM
  your_table
INNER JOIN
  calendar
    ON  calendar.date >= DATEADD(DAY, DATEDIFF(DAY, 0, your_table.logged_id), 0)
    AND calendar.date <  your_table.logged_out

編集

Linear ではなく CTE でのバイナリ成長。 2^100 の日付で妥当な範囲が得られます。