README.md

1. Getting started

Queries and filters

SELECT

SELECT * FROM jobs;

WHERE

SELECT * from jobs
WHERE job_id = 1;

WHERE min_salary > 4000
AND min_salary < 5000;

ORDER BY

SELECT * from jobs
WHERE min_salary > 1000
AND min_salary < 8000
ORDER BY min_salary;

SELECT * from jobs
WHERE min_salary > 1000
AND min_salary < 8000
ORDER BY min_salary DESC;

LIMIT

SELECT * from jobs
WHERE min_salary > 1000
AND min_salary < 8000
ORDER BY min_salary DESC
LIMIT 5;

Aggregations

AVG

SELECT AVG(min_salary) AS avg_min_salary,
AVG(max_salary) AS avg_max_salary
FROM jobs;

COUNT

SELECT COUNT(*) AS total_jobs
FROM jobs;

MAX

SELECT MAX(min_salary) AS max_min_salary,
MAX(max_salary) AS max_max_salary
FROM jobs;

MIN

SELECT MIN(min_salary) AS min_min_salary,
MIN(max_salary) AS min_max_salary
FROM jobs;

Grouping

GROUP BY

SELECT department_id, COUNT(*) AS total_employees
FROM employees
GROUP BY department_id;

HAVING

SELECT department_id, COUNT(*) AS total_employees
FROM employees
GROUP BY department_id
HAVING COUNT(*) > 5;

Joins

INNER JOIN

An inner join will return only the rows that match in both tables.

SELECT * FROM employees
INNER JOIN departments
ON employees.department_id = departments.department_id;

LEFT JOIN

A left join will return all the rows from the left table, and the matched rows from the right table.

In the query below, all the employees will be returned, even if they don't have a department because employees is the left table.

SELECT * FROM employees
LEFT JOIN departments
ON employees.department_id = departments.department_id;

RIGHT JOIN

A right join will return all the rows from the right table, and the matched rows from the left table.

In the query below, all the departments will be returned, even if they don't have an employee because departments is the right table.

SELECT * FROM employees
RIGHT JOIN departments
ON employees.department_id = departments.department_id;