Computer science fundamentals · Lesson 47 of 60 · Concept lesson · Optional

Database fundamentals

A relational database stores data in tables of rows and columns, and relationships link rows in one table to rows in another.

SQL is the language for asking questions of a relational database, such as selecting the rows that match a condition.

NoSQL databases store data in other shapes, such as documents or key-value pairs, and trade some structure for flexibility.

Picture it

users          orders
id name        id user total
1  Ada         7  1    20
2  Mia         8  1    35

orders.user -> users.id

Two tables linked by a relationship. Each order stores the id of the user who made it, so Ada's two orders both point to user 1.

Code example

import sqlite3

db = sqlite3.connect(":memory:")
db.execute("CREATE TABLE users (id INTEGER PRIMARY KEY, name TEXT)")
db.execute("INSERT INTO users (name) VALUES ('Ada'), ('Mia')")
for row in db.execute("SELECT name FROM users WHERE id = 2"):
    print(row[0])

Output: Mia

SQL creates a table, adds rows and selects the row whose id is 2. Python's built-in sqlite3 runs it.

Check yourself

Pick an answer for each question. You can retry as many times as you like.

Loading the questions…