SELECT last_name, job_title FROM employees e JOIN jobs j ON (e.job_id = j.job_id);

SELECT last_name, department_name

FROM employees CROSS JOIN departments;

SELECT first_name, last_name, department_id, department_name

FROM employees JOIN departments

USING (department_id);

SELECT first_name, last_name, job_id, job_title

FROM employees NATURAL JOIN jobs

WHERE department_id > 80;

Returns only matching rows

Returns only unmatched rows

Joins tables using a foreign key

Returns all possible combinations 

FULL OUTER JOIN

INNER JOIN

LEFT JOIN

RIGHT JOIN

It always returns all rows from the table

It cannot use INNER JOIN

It always requires an alias for the table

It only works on numeric columns

SELECT Department_id, AVG(Salary) FROM Employees GROUP BY Department_id;

SELECT Department_id, Salary FROM Employees GROUP BY Department_id;

SELECT Department_id, AVG(Salary) FROM Employees;

SELECT AVG(Salary) GROUP BY Department_id FROM Employees;

SUM

AVG

COUNT

LENGTH