Summary - Constraints
- SQL course
- Beginner
- Lesson 100/115
- 5 min
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.
Practice Summary - Constraints
Create products with id INT PRIMARY KEY, name VARCHAR(100) NOT NULL, price DECIMAL(10,2) CHECK (price > 0).
Starter code
-- summary table
CREATE TABLE productsSample solution
CREATE TABLE products (
id INT PRIMARY KEY,
name VARCHAR(100) NOT NULL,
price DECIMAL(10,2) CHECK (price > 0)
)Expected output
Tablo oluşturuldu
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Which ensures a relation between two tables?
- PRIMARY KEY
- CHECK
- FOREIGN KEY Correct answer
- UNIQUE
Explanation: FOREIGN KEY ensures a relation between tables.
2 Summary - Constraints: match the terms
| Term | Meaning |
|---|---|
PRIMARY KEY |
primary |
UNIQUE |
unique |
CHECK |
check |
FOREIGN KEY |
relation |