[TODAY] Enabling the Mobile Workforce

Not-Null Constraint

Definition - What does Not-Null Constraint mean?

The not-null constraint is a restriction placed on a column in a relational database table. It enforces the condition that, in that column, every row of data must contain a value - it cannot be left blank during insert or update operations. If this column is left blank, this will produce an error message and the entire insert or update operation will fail.

Techopedia explains Not-Null Constraint

Consider a table named CUSTOMER_MASTER that stores customer details for a bank’s database. Every customer must have at least a surname and must belong to a certain gender. The two columns dealing with surname and gender can then be marked as “NOT NULL” when creating the Customer_Master table.

A sample SQL script for doing this is given below:
CREATE TABLE customer_master (
surname CHAR NOT NULL,
firstname CHAR,
date_of_birth DATE NOT NULL,

The not-null constraint is a useful tool for database designers for enforcing business logic. Instead of using programming code to enforce the “must always have a value" concept, they simply use a built-in database feature.

Sometimes the not-null constraint is implicit. When a column is marked as a primary key (see the “custid” column in our example above), it is used to uniquely identify all rows in the table so that they obviously cannot be left blank.

Share this:

Connect with us

Email Newsletter

Join thousands of others with our weekly newsletter

The 4th Era of IT Infrastructure: Superconverged Systems
The 4th Era of IT Infrastructure: Superconverged Systems:
Learn the benefits and limitations of the 3 generations of IT infrastructure – siloed, converged and hyperconverged – and discover how the 4th...
Approaches and Benefits of Network Virtualization
Approaches and Benefits of Network Virtualization:
Businesses today aspire to achieve a software-defined datacenter (SDDC) to enhance business agility and reduce operational complexity. However, the...
Free E-Book: Public Cloud Guide
Free E-Book: Public Cloud Guide:
This white paper is for leaders of Operations, Engineering, or Infrastructure teams who are creating or executing an IT roadmap.
Free Tool: Virtual Health Monitor
Free Tool: Virtual Health Monitor:
Virtual Health Monitor is a free virtualization monitoring and reporting tool for VMware, Hyper-V, RHEV, and XenServer environments.
Free 30 Day Trial – Turbonomic
Free 30 Day Trial – Turbonomic:
Turbonomic delivers an autonomic platform where virtual and cloud environments self-manage in real-time to assure application performance.