Get a list of dates between few dates - sql

Question

There are some quite similar questions, but not the same.
I have to solve the next problem:
From table with such structure
| DATE_FROM | DATE_TO |
|------------|------------|
| 2010-05-17 | 2010-05-19 |
| 2017-01-02 | 2017-01-04 |
| 2017-05-01 | NULL |
| 2017-06-12 | NULL |
I need to get a list like the one below
| DATE_LIST |
|------------|
| 2010-05-17 |
| 2010-05-18 |
| 2010-05-19 |
| 2017-01-02 |
| 2010-01-03 |
| 2010-01-04 |
| 2017-05-01 |
| 2017-06-12 |
How can I get it with SQL? SQL Server 2016.

Answer 1

Another option is with a CROSS APPLY and an ad-hoc tally table
Select Date_List=B.D
from YourTable A
Cross Apply (
Select Top (DateDiff(DAY,[DATE_FROM],IsNull([DATE_TO],[DATE_FROM]))+1) D=DateAdd(DAY,-1+Row_Number() Over (Order By (Select Null)),[DATE_FROM])
From master..spt_values n1,master..spt_values n2
) B
Returns
Date_List
2010-05-17
2010-05-18
2010-05-19
2017-01-02
2017-01-03
2017-01-04
2017-05-01
2017-06-12

Answer 2

One method uses a recursive CTE:
with cte as (
select date_from as date_list, date_to
from t
union all
select dateadd(day, 1, date_from), date_to
from cte
where date_from < date_to
)
select date_list
from cte;
By default, the recursive CTE is limited to a recursive depth of 100 (and then it returns an error). That works for spans of up to 100 days. You can remove the limit with OPTION (MAXRECURSION 0).

Answer 3

Although you could create the date range on the fly in your query, consider creating a permanent calendar table. This will provide better performance and can be extended with other attributes like day of week, fiscal quarter, etc. You can find many examples of loading such a table with an internet search.
Below is an example with 40 years of dates.
--example calendar table load script
CREATE TABLE dbo.Calendar(
CalendarDate date NOT NULL
CONSTRAINT PK_Calendar PRIMARY KEY
);
WITH
t4 AS (SELECT n FROM (VALUES(0),(0),(0),(0)) t(n))
,t256 AS (SELECT 0 AS n FROM t4 AS a CROSS JOIN t4 AS b CROSS JOIN t4 AS c CROSS JOIN t4 AS d)
,t64k AS (SELECT ROW_NUMBER() OVER (ORDER BY (a.n)) AS num FROM t256 AS a CROSS JOIN t256 AS b)
INSERT INTO dbo.Calendar WITH(TABLOCKX)
SELECT DATEADD(day, num, '20000101')
FROM t64k
WHERE DATEADD(day, num, '20000101') < '20400101'
GO
DECLARE #example TABLE(
DATE_FROM date NOT NULL
,DATE_TO date NULL
);
GO
--example query
INSERT INTO #example VALUES
('2010-05-17', '2010-05-19')
, ('2017-01-02', '2017-01-04')
, ('2017-05-01', NULL)
, ('2017-06-12', NULL)
SELECT
c.CalendarDate
FROM #example AS e
JOIN dbo.Calendar AS c ON
c.CalendarDate BETWEEN e.DATE_FROM AND COALESCE(e.DATE_TO, e.DATE_FROM);