How to Handle NULL Values in MariaDB

How do I properly handle NULL values in MariaDB?

NULL-handling lets you test, replace, and compare missing values so queries return the expected rows and calculations.

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Description

Why are NULL values special in MariaDB?

NULL represents "unknown." Any arithmetic or comparison with NULL becomes NULL, and equality operators never match it. Proper handling prevents wrong counts, sums, and joins.

When should I use IS NULL or IS NOT NULL?

Use IS NULL to filter rows lacking a value, and IS NOT NULL to exclude them.Writing email = NULL returns nothing because = never matches NULL.

How do COALESCE and IFNULL replace NULL with defaults?

COALESCE(expr1, …, default) returns the first non-NULL value. IFNULL(expr, default) is a MariaDB shortcut for two parameters. Both turn NULLs into useful defaults like 0 or ''.

What does NULLIF do?

NULLIF(a, b) returns NULL when a = b, otherwise a.Wrap divisors with NULLIF(divisor, 0) to avoid divide-by-zero errors in calculations.

Can I force NULLs to sort last?

ORDER BY column IS NULL, column sorts non-NULLs first regardless of ASC/DESC rules, improving report readability.

Practical ecommerce example

Need customer spending including pending orders? COALESCE(o.total_amount, 0) replaces NULL totals so sums don’t ignore customers with no orders.

Why How to Handle NULL Values in MariaDB is important

How to Handle NULL Values in MariaDB Example Usage


-- Show each customer’s total spend, treating NULL totals as zero
SELECT c.id,
       c.name,
       COALESCE(SUM(o.total_amount), 0) AS lifetime_value
FROM Customers AS c
LEFT JOIN Orders AS o ON o.customer_id = c.id
GROUP BY c.id, c.name
ORDER BY lifetime_value DESC;

How to Handle NULL Values in MariaDB Syntax


-- Detect unknown values
SELECT *
FROM Customers
WHERE email IS NULL;

-- Replace NULL with default
SELECT id,
       COALESCE(total_amount, 0) AS total_amount
FROM Orders;

-- Two-argument shortcut
SELECT IFNULL(stock, 0) AS stock
FROM Products;

-- Prevent divide-by-zero
SELECT order_id,
       total_amount / NULLIF(quantity, 0) AS unit_price
FROM OrderItems;

-- Custom NULL ordering
SELECT name, email
FROM Customers
ORDER BY email IS NULL, email;

Common Mistakes

Using = NULL or <> NULL for comparisons. Fix by replacing with IS NULL or IS NOT NULL because equality operators never match NULL.
Assuming aggregates count NULL rows. COUNT(column) skips NULLs; use COUNT(*) or COALESCE inside SUM/AVG to include them.