sql / intermediate
Snippet
Correlated Subqueries
A correlated subquery references columns from the outer query. It is evaluated once for each row processed by the outer query to perform row-specific logic.
snippet.sql
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SELECT e1.nameFROM employees e1WHERE e1.salary > (SELECT AVG(e2.salary)FROM employees e2WHERE e2.department_id = e1.department_id);
Breakdown
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WHERE e1.salary > (
Initiates a comparison between a row value and the result of the subquery.
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WHERE e2.department_id = e1.department_id
The correlation step that links the subquery to the current outer row's department.