SQL Queries - Advanced SQL | Database Systems

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Sample Database

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Table	Rows	Action
employees	150
departments	12
projects	25

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Interactive SQL Examples

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Basic SELECT Queries

-- Simple selection SELECT first_name, last_name, salary FROM employees WHERE salary > 50000 ORDER BY salary DESC;

JOIN Operations

-- Employee with department info SELECT e.first_name, e.last_name, d.department_name FROM employees e INNER JOIN departments d ON e.department_id = d.department_id;

Aggregate Functions

-- Department statistics SELECT d.department_name, COUNT(*) as employee_count, AVG(e.salary) as avg_salary, MAX(e.salary) as max_salary FROM employees e JOIN departments d ON e.department_id = d.department_id GROUP BY d.department_name;

Subqueries

-- Employees earning above average SELECT first_name, last_name, salary FROM employees WHERE salary > ( SELECT AVG(salary) FROM employees ) ORDER BY salary DESC;

Advanced Filtering

-- Complex WHERE conditions SELECT * FROM employees WHERE (salary BETWEEN 40000 AND 80000) AND (department_id IN (1, 2, 3)) AND (hire_date >= '2020-01-01') AND (first_name LIKE 'J%');

Window Functions

-- Ranking employees by salary within department SELECT first_name, last_name, salary, department_id, RANK() OVER (PARTITION BY department_id ORDER BY salary DESC) as salary_rank FROM employees ORDER BY department_id, salary_rank;

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Interactive SQL Queries