Learn SQL from Scratch

What is SQL?

SQL, or Structured Query Language, is a language designed to manage and manipulate databases.

It is the tool that allows you to store, query, and modify data efficiently.

Components of SQL

One of the main uses of SQL is to perform CRUD operations

Although there are also more advanced operations (such as creating databases or managing permissions and users)

Getting Data

The most basic query in SQL is SELECT, which allows you to extract data from a database.

SELECT * 
FROM employees;

Filtering Data

To get specific data, you can use the WHERE clause to filter results.

SELECT * 
FROM employees 
WHERE age > 30;

Sorting Data

You can sort the results with the ORDER BY clause.

SELECT * 
FROM employees 
ORDER BY salary DESC;

Aggregate Functions

SQL has functions to perform calculations and aggregate data, such as COUNT, SUM, AVG, MIN, and MAX.

SELECT AVG(salary) 
FROM employees;

Table Joins

SQL allows you to combine data from multiple tables using JOIN (there are different types)

SELECT employees.name, departments.name 
FROM employees 
JOIN departments ON employees.dept_id = departments.id;

Inserting Data

To add data to a table, we use the INSERT INTO statement.

INSERT INTO employees (name, salary) 
VALUES ('Ana', 50000);

Updating Data

You can update existing data with the UPDATE statement.

UPDATE employees
SET salary = 55000
WHERE name = 'Ana';

Deleting Data

You can also delete data with the DELETE FROM statement.

DELETE FROM employees 
WHERE name = 'Ana';

Advanced Operations

Besides working with data, there are many more operations you can perform when working with databases.

For example, you can create a new table with CREATE TABLE, or create relationships between tables with FOREIGN KEY. You can even create users or change permissions!