# Find users who have never seen an ad using a LEFT JOIN and NULL check.

Canonical URL: <https://datadriven.io/problems/find-users-who-have-never-seen-an-ad-using-a-left-join-and-n-9e643d66>

Domain: SQL · Difficulty: medium

## Problem

Find users who have never seen an ad using a LEFT JOIN and NULL check.

## Related

- [All practice problems](https://datadriven.io/problems)
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