SQL NULL, IS NULL, and ANSI_NULLS Explained: The Fun Guide Every Developer Needs

Introduction: Why SQL NULL Confuses Even Experienced Developers

If you’ve ever typed SELECT * FROM users WHERE age = NULL; and wondered why it returned nothing, you’re not alone. SQL’s NULL behavior can be tricky, and misunderstanding it often leads to hours of debugging. Don’t worry — we’ll break it down in a fun, easy-to-understand way.

By the end of this post, you’ll know why = NULL fails, how to use IS NULL safely, and what ANSI_NULLS ON/OFF really means.

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Understanding NULL in SQL

In SQL, NULL is not a value; it represents unknown. That’s why using the equality operator doesn’t work:

SELECT * FROM users WHERE age = NULL;

Even if some rows have NULL in the age column, SQL returns zero results. Essentially, SQL treats NULL as an unknown quantity — it cannot confirm equality.

Key takeaway: Never use = NULL for null checks.

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The Correct Way: Using IS NULL

The proper way to check for NULL values is:

SELECT * FROM users WHERE age IS NULL;

This works because IS NULL is designed specifically to test for unknown values.

Why This Matters

• Avoids confusing errors

• Ensures queries return accurate results

• Prevents hours wasted debugging

Pro Tip: Think of IS NULL as the “safe zone” for null checks in SQL.

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ANSI_NULLS: Why ON or OFF Matters

Here’s where it gets interesting. SQL has a setting called ANSI_NULLS.

• ANSI_NULLS ON (default):

  • = NULL will never return true

  • Only IS NULL works

• ANSI_NULLS OFF:

  • Suddenly, = NULL starts returning results

  • But this is dangerous for production environments because it can create inconsistent behavior

SET ANSI_NULLS OFF;
SELECT * FROM users WHERE age = NULL;

Moral of the story: Stick to IS NULL for safe and predictable results.

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Fun Examples of SQL NULL Confusion

1. The “It Works on My Machine” Moment:

SELECT * FROM users WHERE age = NULL;
-- returns 0 rows

2. Finally Getting It Right:

SELECT * FROM users WHERE age IS NULL;
-- returns correct rows

3. When ANSI_NULLS OFF Breaks/Helps:

SET ANSI_NULLS OFF;
SELECT * FROM users WHERE age = NULL;
-- now it returns rows

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Quick Recap

• NULL = unknown, not zero or empty

• Use IS NULL for null checks

• = NULL fails if ANSI_NULLS is ON

• ANSI_NULLS ON/OFF controls how SQL interprets equality with NULL

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Why Understanding NULL Saves Developers Time

SQL can be confusing, but mastering NULL behavior will:

• Prevent countless debugging hours

• Make your queries more reliable

• Give you bragging rights among dev friends 😎

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Conclusion: SQL NULLs Made Fun

SQL might be strict, but it keeps life interesting. Remember: IS NULL is your friend, = NULL is a trap, and ANSI_NULLS is the rulebook. Master these, and you’ll stop pulling your hair out over mysterious query results!

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