SQL IS NULL

The only correct way to check for a missing value — = NULL never works, no matter how tempting it looks.

What & Why

NULL means "no value recorded" — not zero, not an empty string, genuinely absent. IS NULL is the only way to test for it; ordinary comparisons like = NULL never return true, not even when comparing a NULL to itself.

See How It Works

BUSINESS QUESTION

Find product feedback rows where nps_score is missing.

id	user_id	feature_id	rating	nps_score	comment	created_at
1	101	1	5	9	Clear and useful	2024-01-25 12:15:00+00
2	102	2	4	NULL	Export worked well	2024-02-20 15:40:00+00
3	103	1	4	7	Helpful setup flow	2024-03-18 09:05:00+00
4	104	3	3	NULL	Needs clearer timing	2024-04-08 17:30:00+00

Watch is null check each rowRow 1 of 4

-- checking 1: 9 IS NULL?FALSE — dropped

id	nps_score
1	9
2	NULL
3	7
4	NULL

nps_score IS NULL is false for 1.

EXAMPLE QUERY

SELECT id, user_id, rating
FROM product.feedback
WHERE nps_score IS NULL;

Now You Try

Practice this concept

Marketing wants leads that have not converted yet.

Available schema

marketing

Prefix tables with marketing.table_name.

idemailconverted_at

marketing.leads

Column	Type
id	integer
campaign_id	integer
email	text
created_at	timestamp with time zone
qualified_at	timestamp with time zone
converted_at	timestamp with time zone
lead_score	integer
source	text
country	text
archive_status	text

query.sql

Beginner business practice