Introduction to SQL
SQL, which stands for Structured Query Language, is a standardized language for managing and manipulating databases. In simple terms, SQL allows us to query, retrieve, and modify data in our databases.
This language works with various commands, each performing a specific function. For example, the SELECT and INSERT commands are among the most frequently used, which respectively allow retrieving data and adding new data.
Structure of SQL Commands
Understanding the structure of SQL commands can help you leverage its capabilities in the best possible way. It is important to know that SQL is read line by line and executed, and the order of commands is of utmost importance.
To correctly execute commands, you must be familiar with the syntax rules and the meaning of the commands involved. For instance, SELECT, FROM, and WHERE are often used together to query specific information from tables based on particular conditions.
Examples of SQL Commands
-- Retrieve all records from the users table
SELECT * FROM users;
-- Add a new user to the users table
INSERT INTO users (name, email) VALUES ('Ali', '[email protected]');
-- Update the email information of the user
UPDATE users SET email = '[email protected]' WHERE id = 1;
-- Delete a user from the users table
DELETE FROM users WHERE id = 2;
Explanation of SQL Commands
SELECT *: retrieves all columns and records from the table.
FROM users: tells SQL from which table to retrieve the data.
INSERT INTO users: adds a new record to the table.
(name, email): specifies that the columns name and email will be populated.
VALUES('Ali', '[email protected]'): the actual values being assigned to the specified columns.
UPDATE users: indicates that you want to update existing records.
SET email = '[email protected]': specifies the new value for the email column.
WHERE id = 1: this condition specifies that only the record with id equal to 1 should be updated.
DELETE FROM users: removes a record from the table.
WHERE id = 2: specifies which record to delete, in this case, the one with id equal to 2.