Difference between Constraints and Rules in SQL

Question

What is the difference between using constraints and rules in SQL, preferably SQL server 2008 R2. Can anyone explain and demonstrate with a real time example

Answer 1

There are a lot of difference but One the most notable difference is that we can bind rules to a datatypes whereas constraints are bound only to columns. this feature enable us to create our own data-type with the help of Rules and get the input according to that.

I have found a good example, check the following link. constraints vs rules

Answer 2

From Postgres manual:

The PostgreSQL rule system allows one to define an alternate action to be performed on insertions, updates, or deletions in database tables. Roughly speaking, a rule causes additional commands to be executed when a given command on a given table is executed

A constraint, as an example, can be used to ensure that a given number never matches some value. Such a birth year should not be under 1880 for new users registering or above the current year.