Summary - Constraints

Combine UNIQUE, CHECK and FOREIGN KEY to design a table.

Summary - Constraints

In this group you learned PRIMARY KEY, UNIQUE, CHECK and FOREIGN KEY constraints. They are the basis of data integrity.

CREATE TABLE orders (
  id INT PRIMARY KEY,
  customer_id INT,
  total DECIMAL(10,2) CHECK (total >= 0),
  FOREIGN KEY (customer_id) REFERENCES customers(id)
);

A complete table with multiple constraints.

The table orders is created.

Exercise Summary - Constraints

Create products with id INT PRIMARY KEY, name VARCHAR(100) NOT NULL, price DECIMAL(10,2) CHECK (price > 0).

Show example solution

CREATE TABLE products (
  id INT PRIMARY KEY,
  name VARCHAR(100) NOT NULL,
  price DECIMAL(10,2) CHECK (price > 0)
)

Test yourself

Which ensures a relation between two tables?
- PRIMARY KEY
- CHECK
- FOREIGN KEY
- UNIQUE
Show answer

FOREIGN KEY — FOREIGN KEY ensures a relation between tables.
Summary - Constraints: match the terms

PRIMARY KEY

primary
UNIQUE

unique
CHECK

check
FOREIGN KEY

relation

Next lesson: What is JOIN?

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