Subqueries

একটা SQL query-এর ভিতরে আরেকটা query।

Example:

Average salary-এর চেয়ে বেশি salary পাওয়া employees।

SELECT *
FROM employees
WHERE salary > (
    SELECT AVG(salary)
    FROM employees
);

Inner query first:

Average salary

বের করে।

Outer query তার সাথে compare।

CTE Alternative

WITH company_avg AS (
    SELECT
        AVG(salary) AS avg_salary
    FROM employees
)

SELECT *
FROM employees
WHERE salary >
(
    SELECT avg_salary
    FROM company_avg
);

CTE complex query readable করতে খুব useful।