Correlated subquery
Correlated subquery
Correlated subqueries may appear elsewhere besides the WHERE clause; for example, this query uses a correlated subquery in the SELECT clause to print the entire list of employees alongside the average salary for each employee's department.Again, because the subquery is correlated with a column of the outer query, it must be re-executed for each row of the result.
SELECT
employee_number,
name,
(SELECT AVG(salary)
FROM employees
WHERE department = Bob.department) AS department_average
FROM employees AS Bob
group by employee_number,name ;
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