Left Join Nulls — Solution & ExplanationProblems / Left Join Nulls / EditorialApproach

LEFT JOIN employees to projects on emp_id. Every employee is preserved; those without projects get NULLs for project columns.

Filter with WHERE p.project_id IS NULL to keep only unmatched employees.

Select the employee columns and order by emp_id.

Key InsightThe LEFT JOIN + IS NULL pattern is one of the most common ways to find "missing" relationships. It's equivalent to NOT EXISTS or NOT IN but often more readable.Hints

A LEFT JOIN keeps all rows from the left table, filling NULLs for non-matching right-side columns.

Check for NULL on a column from the right table (like project_id) to identify unmatched rows.

This pattern is sometimes called a LEFT ANTI JOIN.

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