Enforcing Event Capacity Limits using Custom Functions with Check Constraints in SQL Server 2008

In SQL Server 2008, ensuring that the expected attendance of events doesn't exceed venue capacities is crucial for planning and resource allocation. To enforce this constraint, a custom function can be employed in conjunction with a check constraint.

The custom function, named CheckVenueCapacity, takes two parameters: @venue_id and @capacity. It compares the specified @capacity with the maximum capacity for the venue with the given @venue_id. If the @capacity is less than or equal to the venue capacity, it returns 0; otherwise, it returns 1.

CREATE FUNCTION dbo.CheckVenueCapacity (@venue_id int, @capacity int)
RETURNS int
AS 
BEGIN
  DECLARE @retval int
  SELECT @retval = CASE WHEN venue_max_capacity >= @capacity THEN 0 ELSE 1 END
  FROM venues
  WHERE venue_id = @venue_id 
  RETURN @retval
END;
GO

To enforce the constraint, a check constraint is added to the events table, ensuring that the expected attendance (event_expected_attendance) for each event satisfies the CheckVenueCapacity function with the event's venue ID (event_venue_id):

ALTER TABLE events
ADD CONSTRAINT chkVenueCapacity 
CHECK (dbo.CheckVenueCapacity(event_venue_id, event_expected_attendance) = 0);

By combining the custom function with a check constraint, the database ensures that event attendance doesn't exceed venue capacities, maintaining data integrity and facilitating event planning with confidence.