How to find the continous range of dates in Sql Server? - sql

Question

How do we find the continous range of dates from the following scenario?
Id modifiedDate StartDate EndDate
1 2019-01-01 2019-01-01 2019-12-31
1 2019-02-02 2019-02-01 2019-02-28
1 2019-02-27 2019-01-15 2019-03-15
1 2019-03-01 2019-03-01 2019-03-12
2 2019-01-01 2019-01-01 2019-03-01
2 2019-05-01 2019-05-01 2019-08-01
The Output i want to show is :
Id StartDate EndDate
1 2019-01-01 2019-01-15
1 2019-01-15 2019-02-01
1 2019-02-01 2019-02-28
1 2019-02-28 2019-03-01
1 2019-03-01 2019-03-12
2 2019-01-01 2019-03-01
2 2019-05-01 2019-08-01
What I have tried so far is :
With X As(
Select a.StartDate,a.EndDate,b.StartDate,b.EndDate
From table a Full Join table b ON a.endDate>b.StartDate
Where a.StartDate<>b.StartDate and b.endDate<>a.Enddate
)
Select StartDate,Enddate,Min(StartDtae)
From X
Group By StartDate,EndDate
But I couldn't get fill the gaps in between the dates. How can I fix this?

Answer 1

You can try this following script I have created with the Help of CTE and Row_Number(). I am getting 2 additional row considering your sample output from the the given input data. If you sample output is correct, you can ignore this solution.
CTE Only worked for MSSQL and Oracle. But you can convert the logic given, for any other databases.
WITH CTE
AS
(
SELECT DISTINCT id,Date, ROW_NUMBER() OVER(PARTITION BY id ORDER BY Date) RN
FROM
(
SELECT Id,StartDate Date FROM your_table
UNION ALL
SELECT Id,EndDate FROM your_table
) A
)
SELECT A.Id, A.Date StartDate,B.Date EndDate
FROM CTE A
INNER JOIN CTE B ON A.Id = B.Id AND A.RN = B.RN - 1
Output is-
Id StartDate EndDate
1 2019-01-01 2019-01-15
1 2019-01-15 2019-02-01
1 2019-02-01 2019-02-28
1 2019-02-28 2019-03-01
1 2019-03-01 2019-03-12
1 2019-03-12 2019-03-15 -- Not exist in your expected output
1 2019-03-15 2019-12-31 -- Not exist in your expected output
Note: Adding an additional Filtering at the as below will give you the exact output you have posted. But take your own decision which one best suits your requirement.
SELECT....
....
FROM CTE A
INNER JOIN CTE B ON A.Id = B.Id AND A.RN = B.RN - 1
WHERE B.DATE <= '2019-03-12'

Answer 2

The following query should give you the desired result:
WITH dates AS (SELECT StartDate
FROM TABLE
UNION
SELECT EndDate + 1
FROM TABLE)
SELECT StartDate
, (SELECT MIN(StartDate) - 1
FROM dates b
WHERE StartDate - 1 > a.StartDate) EndDate
FROM dates a

Answer 3

Just use lead() with union:
select t.id, t.dte as startdate,
lead(t.dte) over (partition by t.id order by t.dte) as enddate
from (select distinct t.id, v.dte
from t cross apply
(values (startdate), (enddate)) v(dte)
) t;
In addition to being concise, this probably has the best performance.