Working with NULL Values in SQL

In SQL and relational databases, NULL values are an important part of managing data and information stored in SQL tables. A NULL value is used as a placeholder for missing values or values that are unknown in a database column or cell.

A NOT NULL Default

The NULL Connection Setting

Case expression with NULL

Missing Data

Missing data is a difficult and common problem to solve. In this article, Joe Celko explains several approaches to deleting or replacing missing data.

What does NULL equal?

Comparing with NULL

Equality on Nullable Columns

CHECK Constraints vs NULL values

Database Design Follies: NULL vs. NOT NULL

It sounds simple enough. Either your column will always have a value or it may not. Yet somehow such a seemingly simple decision can become a never-ending debate where database schema begins to resemble superstition and designing effective tables seems more contentious than you expected it to be.