Data types and constraints in Supabase - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a column with a text data type in Supabase.

Supabase

CREATE TABLE users (username [1] NOT NULL);

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AINTEGER

BVARCHAR(255)

CTEXT

DBOOLEAN

Attempts:

3 left

💡 Hint

Common Mistakes

Using INTEGER or BOOLEAN for text data.

Using VARCHAR without specifying length.

The TEXT data type stores variable-length strings in Supabase.

2fill in blank

medium

Complete the code to add a primary key constraint to the id column.

Supabase

CREATE TABLE products (id [1] PRIMARY KEY, name TEXT);

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ASERIAL

BDATE

CTEXT

DBOOLEAN

Attempts:

3 left

💡 Hint

Common Mistakes

Using TEXT as a primary key without uniqueness.

Using BOOLEAN or DATE for id columns.

The SERIAL type auto-increments integers and is commonly used for primary keys.

3fill in blank

hard

Fix the error in the column definition to correctly enforce a NOT NULL constraint.

Supabase

CREATE TABLE orders (order_id INTEGER [1]);

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AUNIQUE

BNULL

CDEFAULT NULL

DNOT NULL

Attempts:

3 left

💡 Hint

Common Mistakes

Using NULL or DEFAULT NULL which allow empty values.

Confusing UNIQUE with NOT NULL.

The NOT NULL constraint ensures the column cannot have empty values.

4fill in blank

hard

Fill both blanks to create a table with a unique email column and a created_at timestamp with default current time.

Supabase

CREATE TABLE users (email [1] UNIQUE, created_at [2] DEFAULT now());

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ATEXT

BBOOLEAN

CTIMESTAMP

DINTEGER

Attempts:

3 left

💡 Hint

Common Mistakes

Using BOOLEAN or INTEGER for email or timestamp.

Forgetting UNIQUE constraint on email.

Email should be stored as TEXT and timestamps use TIMESTAMP type with default current time.

5fill in blank

hard

Fill all three blanks to define a table with an id primary key, a price column that cannot be negative, and a status column with a default value.

Supabase

CREATE TABLE items (id [1] PRIMARY KEY, price [2] CHECK (price >= 0), status [3] DEFAULT 'available');

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

ASERIAL

BNUMERIC

CTEXT

DBOOLEAN

Attempts:

3 left

💡 Hint

Common Mistakes

Using BOOLEAN for price or status.

Not using CHECK to prevent negative prices.

SERIAL is used for auto-increment id, NUMERIC for price with a check constraint, and TEXT for status with a default value.

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