Table relationships in Supabase - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a foreign key relationship in Supabase SQL.

Supabase

CREATE TABLE orders (id SERIAL PRIMARY KEY, user_id INTEGER [1] REFERENCES users(id));

Drag options to blanks, or click blank then click option'

AFOREIGN KEY

BUNIQUE

CINDEX

DCONSTRAINT

Attempts:

3 left

💡 Hint

Common Mistakes

Using CONSTRAINT without FOREIGN KEY keyword.

Using INDEX or UNIQUE which do not define relationships.

The FOREIGN KEY keyword defines a foreign key relationship linking user_id in orders to id in users.

2fill in blank

medium

Complete the code to create a one-to-many relationship between users and posts.

Supabase

CREATE TABLE posts (id SERIAL PRIMARY KEY, author_id INTEGER [1] users(id));

Drag options to blanks, or click blank then click option'

AREFERENCES

BJOIN

CCONNECTS

DLINKS

Attempts:

3 left

💡 Hint

Common Mistakes

Using JOIN which is for queries, not table definitions.

Using LINKS or CONNECTS which are not SQL keywords.

The REFERENCES keyword creates a foreign key pointing author_id in posts to id in users, establishing a one-to-many relationship.

3fill in blank

hard

Fix the error in the foreign key constraint syntax.

Supabase

ALTER TABLE comments ADD CONSTRAINT fk_post_id FOREIGN KEY (post_id) [1] posts(id);

Drag options to blanks, or click blank then click option'

ALINKS

BCONNECTS

CREFERENCES

DJOINS

Attempts:

3 left

💡 Hint

Common Mistakes

Using LINKS, CONNECTS, or JOINS which are invalid in this context.

The correct syntax uses REFERENCES to specify the referenced table and column in a foreign key constraint.

4fill in blank

hard

Fill both blanks to create a many-to-many relationship using a join table.

Supabase

CREATE TABLE [1] (user_id INTEGER [2] users(id), role_id INTEGER REFERENCES roles(id));

Drag options to blanks, or click blank then click option'

Auser_roles

BREFERENCES

CFOREIGN KEY

Droles_users

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect table names that don't reflect the relationship.

Using FOREIGN KEY keyword alone without REFERENCES.

The join table is commonly named user_roles and the foreign key uses REFERENCES to link user_id to users(id).

5fill in blank

hard

Fill all three blanks to define a composite primary key and foreign keys in a join table.

Supabase

CREATE TABLE [1] (user_id INTEGER [2] users(id), role_id INTEGER REFERENCES roles(id), PRIMARY KEY ([3]));

Drag options to blanks, or click blank then click option'

Auser_roles

BREFERENCES

Cuser_id, role_id

DFOREIGN KEY

Attempts:

3 left

💡 Hint

Common Mistakes

Using FOREIGN KEY keyword without REFERENCES.

Not defining a composite primary key for the join table.

The join table user_roles uses REFERENCES to link foreign keys and defines a composite primary key on user_id, role_id to ensure uniqueness.

Practice

1. What is the main purpose of creating table relationships in Supabase?

easy

A. To store files in the database

B. To connect data across tables using keys

C. To increase the size of the database

D. To change the database theme

Solution

1. Step 1: Understand table relationships

   Table relationships link data in different tables using keys to keep data connected.

2. Step 2: Identify the purpose

   This linking helps to find related data easily, like joining customer info with orders.

3. Final Answer:

   To connect data across tables using keys -> Option B

4. Quick Check:

   Table relationships = Connect data [OK]

Hint: Relationships link tables by keys for easy data access [OK]

Common Mistakes:

• Thinking relationships store files
• Believing relationships increase database size
• Confusing relationships with UI themes

2. Which SQL keyword is used in Supabase to create a foreign key relationship between tables?

easy

A. REFERENCES

B. JOIN

C. SELECT

D. INSERT

Solution

1. Step 1: Identify the keyword for foreign keys

   In SQL, the REFERENCES keyword defines a foreign key that links one table's column to another's primary key.

2. Step 2: Match with Supabase usage

   Supabase uses standard SQL, so REFERENCES is used to create safe links between tables.

3. Final Answer:

   REFERENCES -> Option A

4. Quick Check:

   Foreign key = REFERENCES [OK]

Hint: Use REFERENCES to link tables with foreign keys [OK]

Common Mistakes:

• Using JOIN to create relationships (JOIN reads data, doesn't create keys)
• Confusing SELECT or INSERT with key creation

3. Given these two tables:
CREATE TABLE authors (id SERIAL PRIMARY KEY, name TEXT);
CREATE TABLE books (id SERIAL PRIMARY KEY, title TEXT, author_id INT REFERENCES authors(id));
What will this query return?
SELECT books.title, authors.name FROM books JOIN authors ON books.author_id = authors.id;

medium

A. A list of books without author names

B. A list of authors without book titles

C. An error because of missing foreign key

D. A list of book titles with their author's names

Solution

1. Step 1: Understand the table relationship

   The books table has a foreign key author_id linking to authors.id, connecting each book to its author.

2. Step 2: Analyze the JOIN query

   The query joins books and authors on matching author_id and id, selecting book titles and author names together.

3. Final Answer:

   A list of book titles with their author's names -> Option D

4. Quick Check:

   JOIN on foreign key returns related data [OK]

Hint: JOIN returns combined rows matching foreign keys [OK]

Common Mistakes:

• Expecting authors without books from this JOIN
• Thinking query causes error due to foreign key
• Assuming books without author names appear

4. You wrote this table creation:
CREATE TABLE orders (id SERIAL PRIMARY KEY, customer_id INT, FOREIGN KEY customer_id REFERENCES customers(id));
Why does this cause an error in Supabase?

medium

A. FOREIGN KEY syntax is incorrect; it needs parentheses around the column

B. customer_id must be TEXT, not INT

C. PRIMARY KEY cannot be SERIAL

D. REFERENCES keyword is not supported

Solution

1. Step 1: Check FOREIGN KEY syntax

   The FOREIGN KEY clause requires parentheses around the column name, like FOREIGN KEY (customer_id).

2. Step 2: Confirm other parts

   customer_id as INT is valid, SERIAL primary key is valid, and REFERENCES is supported in Supabase.

3. Final Answer:

   FOREIGN KEY syntax is incorrect; it needs parentheses around the column -> Option A

4. Quick Check:

   FOREIGN KEY syntax = parentheses needed [OK]

Hint: Put column names in parentheses after FOREIGN KEY [OK]

Common Mistakes:

• Omitting parentheses around foreign key column
• Changing data type unnecessarily
• Thinking REFERENCES is unsupported

5. You want to create a many-to-many relationship between students and courses tables in Supabase. Which setup is best?

hard

A. Add a foreign key column in students pointing to courses

B. Add a foreign key column in courses pointing to students

C. Create a join table with student_id and course_id as foreign keys

D. Merge students and courses into one table

Solution

1. Step 1: Understand many-to-many relationships

   Many-to-many means each student can take many courses and each course can have many students.

2. Step 2: Choose the correct design

   Neither students nor courses alone can hold all links. A join table with student_id and course_id foreign keys connects them properly.

3. Final Answer:

   Create a join table with student_id and course_id as foreign keys -> Option C

4. Quick Check:

   Many-to-many = join table with two foreign keys [OK]

Hint: Use a join table for many-to-many links [OK]

Common Mistakes:

• Trying to store many-to-many in one table column
• Merging unrelated tables
• Using one foreign key only