What is SQL? Database basics

What is a database?

A database is a system for organizing and storing data. It's similar to a spreadsheet, but the big difference is that it can search and manage millions of records at high speed.

In an online store like Amazon, for example, all the data about products, users, orders, and inventory is managed in a database.

What is SQL?

SQL (pronounced "S-Q-L" or "sequel") is a language for operating on databases. You can write "get data," "add data," "update data," and "delete data" operations in syntax that reads close to English.

The structure of a table

Data is stored in tables. A table is made up of columns and rows (records).

┌─────┬────────────┬──────────────────────────┬──────────┐
│ id  │ name       │ email                    │ city     │  ← columns
├─────┼────────────┼──────────────────────────┼──────────┤
│  1  │ 田中 太郎  │ tanaka@example.com       │ 東京     │  ← records (rows)
│  2  │ 鈴木 花子  │ suzuki@example.com       │ 大阪     │
└─────┴────────────┴──────────────────────────┴──────────┘

Note: this site's sample database stores Japanese names and city names (like 田中 太郎 and 東京/Tokyo) as the actual data values, since it's the same live sample database used by the Japanese version of this site. You'll see these values in several exercises below.

id is the primary key that uniquely identifies each row. By assigning a number that's never duplicated, you can always pinpoint exactly "which row."

The tables used on this site

This site uses the following 4 tables for learning:

• users — user table (15 records)
• products — product table (10 products)
• orders — order table (15 records)
• order_products — order line-item table (20 records)

Try running the following SQL in the editor on the right:

SELECT * FROM users;