Restrict records

Question

Hi I have the following table for a school management system
CREATE TABLE INCENTIVE
(INCENTIVE_ID NUMBER NOT NULL
,IC_STU_ID NUMBER(10,0)
,IC_CLASS_ID NUMBER(10,0)
I need to restrict the ammount of records created to 5 per class, i have no idea how to do this, i suspect i may need another attribute like something to measure against maybe a date but each class has up to 5 incentives awarded each lesson - no more than 5 allowed, how do i restrict the teachers from adding more than 5??
thanks

Answer 1

  Alter Table incentive
    Add Constraint incentive_c01 Check (incentive_id in (1,2,3,4,5));
is this checking weather an incentive id exists?
it is checking by way if the incentive id is inserted in the range of 1 to 5. if attempted to insert another values other than what was specified in the check constraint it will error out.
the constraints above does not enforce the actual logic of your requirement. it is only good for preventing other values for the specific columns to be inserted into the table. supposed there are two class 1 and 2 and each class has the allowable 5 incentive. now there's an attempt to insert another row which basically has 5 incentive for class 1. the constraint looks only for the incentive and will not prevent a duplicate record which has class 1 and incentive 5 which i think is also what you want to prevent. to prevent it you will need another constraints that are unique rows by way of combination of a columns.
  Alter Table incentive
    Add Constraint incentive_u01 Unique (class_id, incentive_id);
or probably you will also need a trigger to restrict insertion of rows or a logic in your pl/sql code. a constraints has limitation and is specific and you cannot have a logical codes on it. what you will need is a code that checks for some conditions for the transaction or process that will meet your requirements.