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Subquery Usage

src/data/question-groups/sql/content/subquery-usage.md

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A subquery is a query inside another query. It helps when you want to:

  • Filter using aggregated data.
  • Compare a value against a dynamic list.
  • Create a temporary table for use in your main query.

Use cases include checking which employees work in a particular location or identifying orders above a calculated average.

sql
-- Subquery in WHERE clause
SELECT name
FROM employees
WHERE department_id IN (
    SELECT id 
    FROM departments 
    WHERE location = 'New York'
);