Data types and constraints in Supabase - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Data Types in Supabase

Which data type in Supabase is best suited to store a user's email address to ensure it is stored as text and can be indexed efficiently?

A TEXT without length limit

B VARCHAR with a length limit

C INTEGER

D BOOLEAN

💡 Hint

Think about storing strings with a maximum length for emails.

VARCHAR with a length limit is ideal for emails because it stores text efficiently and supports indexing, unlike TEXT which has no length limit and may be less efficient for indexing.

❓ Configuration

intermediate

Applying NOT NULL Constraint

Given a Supabase table for users, which SQL statement correctly adds a NOT NULL constraint to the 'username' column?

A ALTER TABLE users MODIFY username NOT NULL;

B ALTER TABLE users CHANGE username username NOT NULL;

C ALTER TABLE users ALTER COLUMN username SET NOT NULL;

D ALTER TABLE users ADD CONSTRAINT username NOT NULL;

💡 Hint

Focus on the correct syntax for altering a column constraint in PostgreSQL (used by Supabase).

In PostgreSQL, the correct syntax to add a NOT NULL constraint is ALTER TABLE ... ALTER COLUMN ... SET NOT NULL.

❓ Architecture

advanced

Choosing Data Types for Performance

You are designing a Supabase table to store product prices with high precision. Which data type should you choose to avoid rounding errors and maintain accuracy?

A FLOAT

B TEXT

C INTEGER

D DECIMAL or NUMERIC

💡 Hint

Consider data types that store exact numeric values rather than approximate.

DECIMAL or NUMERIC types store exact values with fixed precision, avoiding rounding errors common with FLOAT.

❓ security

advanced

Enforcing Unique Constraints

Which SQL command correctly creates a unique constraint on the 'email' column in a Supabase table to prevent duplicate emails?

A ALTER TABLE users ADD CONSTRAINT unique_email UNIQUE (email);

B ALTER TABLE users MODIFY email UNIQUE;

C ALTER TABLE users ADD UNIQUE (email);

D CREATE UNIQUE INDEX email ON users(email);

💡 Hint

Look for the syntax that names the constraint explicitly.

Adding a named unique constraint uses ADD CONSTRAINT with UNIQUE keyword in PostgreSQL (Supabase).

❓ service_behavior

expert

Behavior of CHECK Constraints on Insert

Consider a Supabase table with a CHECK constraint: CHECK (age >= 18). What happens if you try to insert a row with age = 16?

A The insert fails and raises an error.

B The insert succeeds but sets age to NULL.

C The insert succeeds and ignores the constraint.

D The insert succeeds but logs a warning.

💡 Hint

Think about how constraints enforce data validity strictly.

CHECK constraints prevent invalid data; inserting a row violating the constraint causes an error and the insert fails.

Practice

1. What is the main purpose of data types in a Supabase database table?

easy

A. To specify what kind of data each column can store

B. To control user access to the database

C. To create visual reports from data

D. To backup the database automatically

Solution

1. Step 1: Understand data types role

   Data types define the kind of data a column can hold, like numbers or text.

2. Step 2: Differentiate from other features

   Access control, reports, and backups are unrelated to data types.

3. Final Answer:

   To specify what kind of data each column can store -> Option A

4. Quick Check:

   Data types = specify data kind [OK]

Hint: Data types tell what data fits in each column [OK]

Common Mistakes:

• Confusing data types with user permissions
• Thinking data types create reports
• Assuming data types handle backups

2. Which of the following is the correct way to define a column with a NOT NULL constraint in Supabase SQL?

easy

A. username TEXT NOT NULL

B. username NOT NULL TEXT

C. NOT NULL username TEXT

D. TEXT username NOT NULL

Solution

1. Step 1: Recall SQL column definition order

   The correct order is: column name, data type, then constraints.

2. Step 2: Match the syntax

   username TEXT NOT NULL follows this order: username TEXT NOT NULL.

3. Final Answer:

   username TEXT NOT NULL -> Option A

4. Quick Check:

   Column name + type + constraint = correct syntax [OK]

Hint: Column name first, then type, then constraints [OK]

Common Mistakes:

• Placing NOT NULL before the column name
• Swapping data type and constraint order
• Using incorrect keyword order

3. Given the table definition:

CREATE TABLE users (id SERIAL PRIMARY KEY, email TEXT UNIQUE NOT NULL, age INT);

What happens if you try to insert two rows with the same email?

medium

A. The second insert overwrites the first row

B. Both rows are inserted successfully

C. The second insert fails due to UNIQUE constraint violation

D. The database ignores the UNIQUE constraint

Solution

1. Step 1: Understand UNIQUE constraint effect

   The UNIQUE constraint prevents duplicate values in the email column.

2. Step 2: Predict insert behavior

   Inserting a duplicate email causes the second insert to fail with an error.

3. Final Answer:

   The second insert fails due to UNIQUE constraint violation -> Option C

4. Quick Check:

   UNIQUE prevents duplicates = second insert fails [OK]

Hint: UNIQUE means no duplicate values allowed [OK]

Common Mistakes:

• Assuming duplicates are allowed
• Thinking second insert overwrites first
• Ignoring constraint errors

4. You wrote this table definition:

CREATE TABLE products (id INT PRIMARY KEY, name TEXT NOT NULL, price TEXT);

What is the main issue with this definition?

medium

A. The id column cannot be INT

B. The price column should not be TEXT for numeric values

C. The name column cannot have NOT NULL constraint

D. PRIMARY KEY cannot be on id column

Solution

1. Step 1: Check data type appropriateness

   Price should be a numeric type (like INT or NUMERIC), not TEXT, to store numbers properly.

2. Step 2: Validate other columns

   id as INT with PRIMARY KEY and name as TEXT NOT NULL are valid.

3. Final Answer:

   The price column should not be TEXT for numeric values -> Option B

4. Quick Check:

   Price needs numeric type, not text [OK]

Hint: Use numeric types for numbers, not TEXT [OK]

Common Mistakes:

• Using TEXT for numeric columns
• Thinking PRIMARY KEY can't be INT
• Believing NOT NULL is invalid on text

5. You want to create a table to store user profiles with these rules:
- Each user has a unique ID
- Email must be unique and not empty
- Age must be a positive integer or NULL if unknown

Which table definition correctly applies data types and constraints?

hard

A. CREATE TABLE profiles (user_id UUID PRIMARY KEY, email TEXT UNIQUE NOT NULL, age INT CHECK (age > 0) OR age IS NULL);

B. CREATE TABLE profiles (user_id INT, email TEXT NOT NULL, age INT NOT NULL CHECK (age >= 0));

C. CREATE TABLE profiles (user_id UUID PRIMARY KEY, email TEXT UNIQUE NOT NULL, age INT CHECK (age > 0) NOT NULL);

D. CREATE TABLE profiles (user_id UUID PRIMARY KEY, email TEXT UNIQUE NOT NULL, age INT CHECK (age > 0));

Solution

1. Step 1: Check unique ID and email constraints

   CREATE TABLE profiles (user_id UUID PRIMARY KEY, email TEXT UNIQUE NOT NULL, age INT CHECK (age > 0));

   uses UUID PRIMARY KEY for unique ID and email TEXT UNIQUE NOT NULL, which is correct.

2. Step 2: Validate age constraint

   CREATE TABLE profiles (user_id UUID PRIMARY KEY, email TEXT UNIQUE NOT NULL, age INT CHECK (age > 0));

   uses CHECK (age > 0) allowing NULL by default, which fits the requirement.

3. Step 3: Review other options

   CREATE TABLE profiles (user_id INT, email TEXT NOT NULL, age INT NOT NULL CHECK (age >= 0));

   lacks PRIMARY KEY and UNIQUE on email, makes age NOT NULL; C adds NOT NULL to age preventing NULL values; D has syntax error in CHECK constraint.

4. Final Answer:

   CREATE TABLE profiles (user_id UUID PRIMARY KEY, email TEXT UNIQUE NOT NULL, age INT CHECK (age > 0)); -> Option D

5. Quick Check:

   UUID PK, UNIQUE email, age > 0 or NULL = correct [OK]

Hint: Use CHECK for age and UNIQUE + NOT NULL for email [OK]

Common Mistakes:

• Forgetting PRIMARY KEY on user_id
• Making age NOT NULL when it can be NULL
• Writing invalid CHECK constraints