Home/ Questions/Q 9007443
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-06-16T01:41:29+00:00

Is database derived value the same as foreign key? Based on connoly and begg

  • 0

Is database derived value the same as foreign key?

Based on connoly and begg books, fourth edition page 352 derived value is
An attribute that represents a value that is derivable from the value of a related attribute or set of attributes, not necessarily in the same entity type.

If we have 2 table such as, CUSTOMER and ORDER, 

Customer
- Id_Cust
- Name
- Phone

ORDER
- Order_id<
- id_cust

Can we say “ORDER.id_cust is derived from Customer.id_cust” ?

Actually, I’m really confused about the concept above.

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    No, foreign keys and derived values are two different things.

    product  quantity  price  subtotal
--
ACH123   5         $1.50  $7.50

    In the simplified table above, “subtotal” is a derived value. It’s derived from “quantity” and “price”. (By multiplying them together.)

    Database designers usually don’t store derived values without using a CHECK() constraint or a trigger to make sure the derived value is always correct. In the table above, updating the quantity to 4 would make the derived value “subtotal” incorrect. A CHECK() constraint can prevent an update to “quantity” unless the update also has the correct value for “subtotal”. A trigger can automatically update “subtotal” when either “quantity” or “price” changes.

    CHECK() constraints are usually a better choice.

    • 0