CHECK

A check constraint will prevent values outside the bounds of a check.
Lets say you want to ensure that all Prices entered into this table are greater than 10.

Applying After Creation

ALTER TABLE MyProducts 
ADD CONSTRAINT Constraint.Name CHECK (Price > 10) 

Applying On Creation

CREATE TABLE MyProducts 
( 
   ProductValue INTEGER CONSTRAINT constraint.name CHECK (ProductValue BETWEEN 1 AND 100) 
)