Trigger: BEFORE INSERT - sql

Question

How to check if a DATE being inserted or updated in a table is between two other dates from another table.
Adicional Info:
I have 2 tables:
Activity:
StartDate date NOT NULL
EndDate date NULLABLE
SubActivity:
SubActivityDate date NOT NULL
When EndDate IS NOT NULL I check if: StartDate ≤ SubActivityDate ≤ EndDate
When EndDate IS NULL I check if: StartDate ≤ SubActivityDate
I was trying to write a BEFORE INSERT trigger but I figured out that it doesnt exist.
So what I could do?
AFTER INSERT?
INSTEAD OF INSERT? looks better than 1st solution
Is it possible just with CHECK Constraints?
How do I solve this problem?
EDIT
I just went with the CHECK constraint + function:
constraint:
ALTER TABLE SubActivity
ADD CONSTRAINT CK_SubActivity_Date CHECK (dbo.ufnIsSubactivityDateValid(ActivityID, SubActivityDate) = 1);
function:
CREATE FUNCTION ufnIsSubactivityDateValid(#ActivityID [int], #SubActivityDate [date])
RETURNS [bit]
AS
BEGIN
DECLARE #StartDate date, #EndDate date;
SELECT #StartDate = StartDate , #EndDate = EndDate
FROM Activity
WHERE ActivityID = #ActivityID;
IF (#SubActivityDate < #StartDate )
RETURN 0; -- out of range date
IF (#EndDate IS NULL)
RETURN 1; -- good date
ELSE
IF (#SubActivityDate > #EndDate)
RETURN 0; -- out of range date
RETURN 1; -- good date
END

Answer 1

What is best is situation by situation. Constraint guarantees proper values but rollsback an entire transaction over one wrong value. Triggers allow you more control but are a little more complex because of it.
Create and Populate your Table
IF OBJECT_ID('dbo.yourTable') IS NOT NULL
DROP TABLE yourTable;
CREATE TABLE yourTable
(
ID INT IDENTITY(1,1) PRIMARY KEY,
StartDate DATE NOT NULL,
SubActivityDate DATE NULL,
EndDate DATE NULL
);
INSERT INTO yourTable(StartDate,SubActivityDate,EndDate)
VALUES ('20150101',NULL,NULL),
('20150101',NULL,NULL),
('20150101',NULL,'20150201'),
('20150101',NULL,'20150201');
Constraint Method:
ALTER TABLE yourTable
ADD CONSTRAINT chk_date CHECK (StartDate <= SubActivityDate AND SubActivityDate <= EndDate);
UPDATE yourTable
SET SubActivityDate = CASE
WHEN ID = 1 THEN '20140101' --bad
WHEN ID = 2 THEN '20150102' --good
WHEN ID = 3 THEN '20140101' --bad
WHEN ID = 4 THEN '20150102' --good
END
SELECT *
FROM yourTable;
Since there is at least value that does not fit the constraint, the whole transaction is rolled back and the result is that SubActivitDate stays NULL.
Results:
ID StartDate SubActivityDate EndDate
----------- ---------- --------------- ----------
1 2015-01-01 NULL NULL
2 2015-01-01 NULL NULL
3 2015-01-01 NULL 2015-02-01
4 2015-01-01 NULL 2015-02-01
Trigger Method(My Preferred Method)
CREATE TRIGGER trg_check_date ON yourTable
INSTEAD OF UPDATE
AS
BEGIN
UPDATE yourTable
SET SubActivityDate = CASE
WHEN inserted.SubActivityDate >= inserted.StartDate AND ((Inserted.EndDate IS NULL) OR Inserted.SubActivityDate <= Inserted.EndDate) THEN inserted.SubActivityDate
ELSE NULL
END
FROM yourTable
INNER JOIN inserted
ON yourTable.ID = inserted.ID
END;
GO
UPDATE yourTable
SET SubActivityDate = CASE
WHEN ID = 1 THEN '20140101' --bad
WHEN ID = 2 THEN '20150102' --good
WHEN ID = 3 THEN '20140101' --bad
WHEN ID = 4 THEN '20150102' --good
END
SELECT *
FROM yourTable
This method allows the proper values and simply returns null for improper ones. If you wanted, you could even export the incorrect values from the inserted table into a log table so you know which ones didn't work. Or raise an error message and list the values that didn't work. In short, you have total control of the situation.
Results:
ID StartDate SubActivityDate EndDate
----------- ---------- --------------- ----------
1 2015-01-01 NULL NULL
2 2015-01-01 2015-01-02 NULL
3 2015-01-01 NULL 2015-02-01
4 2015-01-01 2015-01-02 2015-02-01

Answer 2

constraint:
ALTER TABLE SubActivity
ADD CONSTRAINT CK_SubActivity_Date CHECK (dbo.ufnIsSubactivityDateValid(ActivityID, SubActivityDate) = 1);
function:
CREATE FUNCTION ufnIsSubactivityDateValid(#ActivityID [int], #SubActivityDate [date])
RETURNS [bit]
AS
BEGIN
DECLARE #StartDate date, #EndDate date;
SELECT #StartDate = StartDate , #EndDate = EndDate
FROM Activity
WHERE ActivityID = #ActivityID;
IF (#SubActivityDate < #StartDate )
RETURN 0; -- out of range date
IF (#EndDate IS NULL)
RETURN 1; -- good date
ELSE
IF (#SubActivityDate > #EndDate)
RETURN 0; -- out of range date
RETURN 1; -- good date
END