How SQL communicates with the database engine

Introduction

SQL is a language that helps you talk to a database. It sends your requests to the database engine, which understands and acts on them.

When you want to get information from a database, like finding all customers in a city.

When you need to add new data, like saving a new order.

When you want to change existing data, like updating a phone number.

When you want to remove data, like deleting old records.

When you want to organize or sort data to see it clearly.

Syntax

SQL

SQL statements are sent as text commands to the database engine.

Example:
SELECT column_name FROM table_name WHERE condition;

SQL commands are plain text and follow a specific structure.

The database engine reads these commands, processes them, and returns results.

Examples

This command asks the database engine to return all data from the 'employees' table.

SQL

SELECT * FROM employees;

This command tells the database engine to add a new customer named Alice from Paris.

SQL

INSERT INTO customers (name, city) VALUES ('Alice', 'Paris');

This command asks the database engine to change the price of the product with id 5 to 10.

SQL

UPDATE products SET price = 10 WHERE id = 5;

This command tells the database engine to remove orders made before January 1, 2023.

SQL

DELETE FROM orders WHERE order_date < '2023-01-01';

Sample Program

This query asks the database engine to find all customers who live in Paris and show their names and cities.

SQL

SELECT name, city FROM customers WHERE city = 'Paris';

Important Notes

The database engine processes SQL commands step-by-step to get the results.

SQL commands must be written correctly for the database engine to understand them.

Different database systems may have small differences, but the main idea of communication stays the same.

Summary

SQL is the language used to send instructions to the database engine.

The database engine reads and executes these instructions to manage data.

Writing clear SQL commands helps the database engine give you the right answers.