Check for Overlapping date on Insert/Update - sql-server

Question

I have a table which holds a list of dates and more data for a person. The table should never have any undeleted overlapping rows (Dates overlapping).
Is there a way I can put a check constraint on the table, to ensure that when I update or insert a row, that there's no overlapping details?
Below is a cut down version of my table. It has a deleted flag, and start/end dates. A 'Null' end date means it's ongoing.
I then provide some legal, and some not-so-legal inserts (and why they're legal and illegal).
DECLARE #Test TABLE
(
Id INT NOT NULL IDENTITY(1,1),
PersonID INT NOT NULL,
StartDate DATE NOT NULL,
EndDate DATE NULL,
Deleted BIT NOT NULL
)
INSERT INTO #Test
(PersonId, StartDate, EndDate, Deleted)
SELECT 1, '01-JAN-2015', '15-JAN-2015', 0 UNION ALL -- Valid
SELECT 1, '16-JAN-2015', '20-JAN-2015', 1 UNION ALL -- Valid and deleted
SELECT 1, '18-JAN-2015', NULL, 0 UNION ALL -- Valid
SELECT 2, '01-JAN-2015', NULL, 0 UNION ALL -- Valid.. never ending row.
SELECT 2, '18-JAN-2015', '30-JAN-2015', 0 UNION ALL -- Invalid! Overlaps above record.
SELECT 2, '20-JAN-2015', '30-JAN-2015', 1 UNION ALL -- Valid, as it's deleted (Still overlaps, though)
SELECT 3, '01-JAN-2015', '10-JAN-2015', 0 UNION ALL -- Valid
SELECT 3, '10-JAN-2015', NULL, 0 -- Invalid, as it overlaps the last and first days
SELECT * FROM #Test
I need to make sure that the table doesn't allow overlapping dates for the same person, for undeleted rows.
For the date range check, I will use the "(StartA <= EndB) and (EndA >= StartB)" formula, but unsure how to check this with a constraint, and across multiple rows.
I may need to do it with a Trigger, by checking the inserted.values to the exiting, and somehow, cancel if I find matches?

Answer 1

you cannot use a CHECK Constraint without adding additional columns.
you will have to create a Trigger to check if inserted date ranges are non overlapping. Something like this..
CREATE TRIGGER [dbo].[DateRangeTrigger]
ON [dbo].Test AFTER INSERT, UPDATE
AS
BEGIN
DECLARE #MaxDate DATE = '2999/12/31'
IF EXISTS (SELECT t.StartDate, t.EndDate FROM Test t
Join inserted i
On i.PersonID = t.PersonID
AND i.id <> t.Id
AND(
(i.StartDate > t.StartDate AND i.StartDate < ISNULL(t.EndDate,#MaxDate))
OR (ISNULL(i.EndDate,#MaxDate) < ISNULL(t.EndDate,#MaxDate) AND ISNULL(i.EndDate,#MaxDate) > t.StartDate)
OR (i.StartDate < t.StartDate AND ISNULL(i.EndDate,#MaxDate) > ISNULL(t.EndDate,#MaxDate))
)
WHERE t.Deleted = 0 AND i.Deleted = 0
)
BEGIN
RAISERROR ('Inserted date was within invalid range', 16, 1)
IF (##TRANCOUNT>0)
ROLLBACK
END
END
You can refer to one of these threads for more information
Enforcing unique date range fields in SQL Server 2008
Unique date range fields in SQL Server 2008

Answer 2

Here's a trigger-based approach:
CREATE TRIGGER [dbo].[trigPersonnel_PreventOverlaps]
ON [dbo].[Personnel]
AFTER INSERT, UPDATE
AS
BEGIN
IF EXISTS(
SELECT * FROM DateRange p
INNER JOIN inserted i ON i.PersonID = p.PersonID
AND i.Id != p.Id AND i.Deleted = 0
AND (
(p.StartDate <= i.StartDate
AND (i.StartDate <= p.EndDate OR p.EndDate IS NULL))
OR (p.StartDate <= i.EndDate
AND (i.EndDate <= p.EndDate OR p.EndDate IS NULL))
)
WHERE p.Deleted = 0
)
--RAISEERROR if you want
ROLLBACK
END
Note - it will roll back the whole transaction, so you'll need to perform inserts individually to ensure good ones don't get thrown out.
If you need something to comb through a bulk insert and pick out the bad ones, you'll need something more complex.