Universal Database (netDB2) Introductory Guide

Working With Constraints

Constraints:
We can add constraints to the database created inorder to add limitations to the database. For example:

In such cases, one can put checks using constraints. The constraints can be put in a table or can be implemented using a "Alter" statement or set statement.

Example:

CREATE TABLE constraint_check (ID SMALLINT NOT NULL, NAME VARCHAR(9), HIREDATE DATE, SALARY DECIMAL(7,2), PRIMARY KEY (ID), CONSTRAINT YEARSAL CHECK (YEAR(HIREDATE) >= 1990 OR SALARY > 20000) )

This particular check implements that the year of hire should be greater than 1990 and also that the salary one is earning has to be 20,000 dollars.

Example:

ALTER TABLE school ADD CONSTRAINT age_check CHECK (age > 5)

This example checks the age of student, by adding a constraint to a table.