Why NULL Handling Can Break Your Logic in SQL

When you first start working with SQL, it feels straightforward — tables, rows, columns, queries. But then you meet NULL.

At first, NULL looks harmless.
It’s “just a missing value,” right?
But here’s the thing — NULL in SQL isn’t zero.
It isn’t an empty string.
It isn’t even “blank.”

It’s unknown.

And that tiny difference can completely change how your queries behave, cause subtle bugs, and even break business logic in ways that are very hard to debug.

In this article, we’ll dive deep into:

• What NULL actually means in SQL
• The rules that make NULL behave differently
• Common mistakes developers make with NULL
• Best practices for handling NULLs in queries
• Real-world scenarios where NULL can cause trouble

1. What NULL Actually Means in SQL

In SQL, NULL represents missing, undefined, or unknown data.
It’s not a value — it’s the absence of a value.

Examples:

• A customer’s phone number field might be NULL if they haven’t…