Question

I have a Table called Couple which has the following Fields CoupleId, HusbandId , WifeId ,
StartDate , EndDate

The previous Table contains informations about couple, The CoupleId is a primary key

HusbandId and WifeId are Foreign keys form another Table Named Person

StartDate and EndDate represent the start/end date of marriage that happens between a male with HusbandId and female with WifeId

in my problem i have a condition that w female can’t married to two or more male at same time “Synchronous marriage”

and i have the following query

SELECT
   DISTINCT A.WifeID
FROM
   Couple A
   INNER JOIN Couple B
      ON A.WifeID = B.WifeID
      AND A.HusbandID <> B.HusbandID
      AND A.StartDate < B.EndDate
      AND A.EndDate > B.StartDate;

which returns any female who has Synchronous marriage ” Married to two or more male at same time”

I want to write trigger which fire when somebody want to insert or update the couple
table ,and i want this trigger allow the modification only if it make no fault information on it ( for example if someone insert a row on couple table and this row make the wife with #4 married to tow or more person at same time, this insertion must not complete because it make wrong info in the table)

can any one help me at this point ?

Answer 1

You can solve this without a trigger. Make a Composite primary key of these three keys in the Couples table like so:

PRIMARY KEY(CoupleId, HusbandId, WifeId)

This will ensure the uniqueness of the HusbandId and WifeId for each coupleId.

Here is a demo for the schema design for these two tables:

SQL Fiddle Demo.

---

If you want to do this using a TRIGGER, try this:

CREATE TRIGGER WhenInsertOrUpdate
ON Couples
INSTEAD OF INSERT, UPDATE
AS 
     IF (NOT EXISTS( SELECT c.CoupleId
                     FROM Couples c
                     INNER JOIN Inserted i  ON c.HusbandId = i.HusbandId
                                           AND c.WifeId = i.WifeId
                                           AND c.EndDate IS NULL))
    BEGIN
       INSERT INTO Couples
       SELECT  CoupleId, HusbandId, WifeId, StartDate, Enddate
       FROM Inserted
    END
    ELSE BEGIN
       --- You can put here an update..
    END

GO;

Updated SQL Fiddle Demo using a trigger.

This is just an example, you have to provide an update statement in the ELSE block if you need.