Creating tables via SQL editor in Supabase - Practice Exercises

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding SQL Table Creation Syntax

What will be the result of running this SQL command in Supabase SQL editor?

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

Supabase

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

A A table named 'users' is created but 'email' column allows duplicate values.

B A new table named 'users' is created with three columns: 'id' as auto-incrementing primary key, 'name' as required text, and 'email' as unique text.

C An error occurs because 'SERIAL' is not supported in Supabase SQL editor.

D The table is created but 'id' column is not set as primary key.

💡 Hint

Check the meaning of 'SERIAL', 'PRIMARY KEY', 'NOT NULL', and 'UNIQUE' in SQL.

This command creates a table 'users' with 'id' as an auto-incrementing primary key, 'name' as a required text field, and 'email' as a unique text field. 'SERIAL' is supported in PostgreSQL, which Supabase uses.

❓ Configuration

intermediate

Identifying Error in Table Creation

What error will this SQL command produce when run in Supabase SQL editor?

CREATE TABLE products (product_id INT PRIMARY KEY, name VARCHAR, price DECIMAL(10));

Supabase

CREATE TABLE products (product_id INT PRIMARY KEY, name VARCHAR, price DECIMAL(10));

A Error because PRIMARY KEY cannot be assigned to INT type.

B Error because DECIMAL requires two parameters for precision and scale.

C Syntax error because VARCHAR requires a length specification.

D Table created successfully with columns 'product_id', 'name', and 'price'.

💡 Hint

In PostgreSQL, VARCHAR without a length specifier is valid and equivalent to TEXT.

In PostgreSQL, VARCHAR without length is valid (unlimited length, equivalent to TEXT). DECIMAL(10) is valid (precision 10, scale 0). The table is created successfully.

❓ Architecture

advanced

Choosing Best Primary Key Design

You want to create a table 'orders' in Supabase to store order data. Which option is the best design for the primary key column?

A Use a column 'order_id' with type UUID generated by default with gen_random_uuid() function.

B Use a composite primary key of 'user_id' and 'order_date' columns.

C Use a text column 'order_code' where users manually enter unique codes.

D Use an integer column 'order_number' with auto-increment (SERIAL) as primary key.

💡 Hint

Consider uniqueness, scalability, and ease of use for primary keys.

UUIDs generated by gen_random_uuid() provide globally unique identifiers, avoid collisions, and are recommended for distributed systems like Supabase. Auto-increment integers can cause issues in distributed environments. Manual text keys risk duplicates. Composite keys add complexity.

❓ security

advanced

Preventing SQL Injection in Table Creation Scripts

Which practice helps prevent SQL injection when creating tables via Supabase SQL editor?

A Never accept user input directly in SQL commands; use parameterized queries or predefined scripts.

B Escape all single quotes in user input manually before inserting into SQL commands.

C Use dynamic SQL concatenation with user input but sanitize inputs with regex.

D Allow users to write their own SQL commands to create tables for flexibility.

💡 Hint

Think about how SQL injection happens and how to avoid it.

SQL injection occurs when user input is directly included in SQL commands. Using parameterized queries or predefined scripts avoids this risk. Manual escaping or regex sanitization is error-prone. Allowing users to write SQL is unsafe.

❓ service_behavior

expert

Effect of Dropping a Table with Dependent Foreign Keys

Given two tables in Supabase:

CREATE TABLE customers (id UUID PRIMARY KEY, name TEXT); CREATE TABLE orders (id UUID PRIMARY KEY, customer_id UUID REFERENCES customers(id));

What happens if you run DROP TABLE customers; without any additional options?

Supabase

DROP TABLE customers;

A The 'customers' table is dropped and 'orders' table remains unchanged with broken foreign key references.

B The 'customers' table is dropped and foreign key constraints in 'orders' are automatically removed.

C The command fails with an error because 'orders' table depends on 'customers' via foreign key.

D The 'customers' table is dropped and all rows in 'orders' with matching customer_id are automatically deleted.

💡 Hint

Consider how foreign key constraints affect dropping tables in PostgreSQL (used by Supabase).

PostgreSQL prevents dropping a table if other tables have foreign key constraints referencing it, unless you use CASCADE option. Without CASCADE, DROP TABLE fails with an error.

Practice

1. What is the main purpose of the CREATE TABLE statement in Supabase SQL editor?

easy

A. To insert data into an existing table

B. To delete an existing table from the database

C. To update data in an existing table

D. To create a new table with specified columns and data types

Solution

1. Step 1: Understand the purpose of CREATE TABLE

   The CREATE TABLE command is used to make a new table structure in the database.

2. Step 2: Differentiate from other SQL commands

   Deleting, inserting, or updating data uses different commands like DROP TABLE, INSERT INTO, or UPDATE.

3. Final Answer:

   To create a new table with specified columns and data types -> Option D

4. Quick Check:

   CREATE TABLE means create table [OK]

Hint: Remember: CREATE TABLE makes new tables, not data changes [OK]

Common Mistakes:

• Confusing CREATE TABLE with INSERT or UPDATE commands
• Thinking CREATE TABLE deletes tables
• Assuming CREATE TABLE modifies existing data

2. Which of the following is the correct syntax to create a table named users with columns id (integer) and email (text) in Supabase SQL editor?

easy

A. CREATE users TABLE (id INT, email STRING);

B. CREATE TABLE users (id INTEGER, email TEXT);

C. TABLE CREATE users (id INT, email TEXT);

D. CREATE TABLE users id INTEGER, email TEXT;

Solution

1. Step 1: Check the correct SQL syntax for table creation

   The correct syntax is CREATE TABLE table_name (column_name data_type, ...); with parentheses around columns.

2. Step 2: Validate data types and order

   Use INTEGER and TEXT as valid data types. The statement must start with CREATE TABLE followed by the table name.

3. Final Answer:

   CREATE TABLE users (id INTEGER, email TEXT); -> Option B

4. Quick Check:

   Correct SQL syntax = CREATE TABLE users (id INTEGER, email TEXT); [OK]

Hint: Use parentheses and correct data types for columns [OK]

Common Mistakes:

• Missing parentheses around columns
• Wrong order of keywords
• Using invalid data types like STRING instead of TEXT

3. Given the SQL command:

CREATE TABLE products (product_id SERIAL PRIMARY KEY, name TEXT NOT NULL, price NUMERIC);

What will be the behavior of the product_id column?

medium

A. It stores text values

B. It must be manually entered for each new product

C. It will automatically generate a unique number for each new row

D. It allows duplicate values

Solution

1. Step 1: Understand the SERIAL PRIMARY KEY usage

   The SERIAL type auto-increments numbers for new rows, and PRIMARY KEY ensures uniqueness.

2. Step 2: Analyze column behavior

   Because of SERIAL PRIMARY KEY, product_id auto-generates unique numbers; manual entry is not required.

3. Final Answer:

   It will automatically generate a unique number for each new row -> Option C

4. Quick Check:

   SERIAL PRIMARY KEY = auto unique number [OK]

Hint: PRIMARY KEY with SERIAL auto-increments IDs [OK]

Common Mistakes:

• Thinking SERIAL requires manual input
• Assuming duplicates are allowed in PRIMARY KEY
• Confusing data types for this column

4. You wrote this SQL to create a table:

CREATE TABLE orders (order_id INT PRIMARY KEY, order_date DATE, customer_id INT);

The table creates successfully, but when inserting rows without specifying order_id, Supabase gives an error. What is the most likely cause?

medium

A. No SERIAL type for auto-incrementing primary key

B. Missing semicolon at the end of the statement

C. No column defined as UNIQUE

D. Using INT instead of INTEGER for data type

Solution

1. Step 1: Check the primary key column definition

   The order_id is INT PRIMARY KEY but lacks auto-increment, so inserting rows without specifying order_id causes errors.

2. Step 2: Understand SERIAL usage for auto-increment

   Using SERIAL instead of INT for primary key allows automatic unique number generation, preventing insert errors.

3. Final Answer:

   No SERIAL type for auto-incrementing primary key -> Option A

4. Quick Check:

   Primary key needs SERIAL for auto-increment [OK]

Hint: Use SERIAL for auto-increment primary keys [OK]

Common Mistakes:

• Assuming INT auto-increments automatically
• Ignoring missing semicolon errors
• Confusing UNIQUE with PRIMARY KEY requirements

5. You want to create a table employees with columns id (auto-incrementing primary key), name (text, required), and email (text, unique). Which SQL command correctly achieves this in Supabase?

hard

A. CREATE TABLE employees (id SERIAL PRIMARY KEY, name TEXT NOT NULL, email TEXT UNIQUE);

B. CREATE TABLE employees (id INT PRIMARY KEY, name TEXT, email TEXT UNIQUE NOT NULL);

C. CREATE TABLE employees (id SERIAL, name TEXT NOT NULL, email TEXT);

D. CREATE TABLE employees (id INTEGER PRIMARY KEY, name TEXT NOT NULL, email TEXT UNIQUE);

Solution

1. Step 1: Define auto-incrementing primary key

   Use SERIAL PRIMARY KEY for id to auto-generate unique IDs.

2. Step 2: Set constraints for name and email

   name must be NOT NULL to be required; email must be UNIQUE to avoid duplicates.

3. Step 3: Verify all constraints and syntax

   CREATE TABLE employees (id SERIAL PRIMARY KEY, name TEXT NOT NULL, email TEXT UNIQUE); correctly includes all required constraints and syntax.

4. Final Answer:

   CREATE TABLE employees (id SERIAL PRIMARY KEY, name TEXT NOT NULL, email TEXT UNIQUE); -> Option A

5. Quick Check:

   Auto-increment + NOT NULL + UNIQUE = CREATE TABLE employees (id SERIAL PRIMARY KEY, name TEXT NOT NULL, email TEXT UNIQUE); [OK]

Hint: Combine SERIAL, NOT NULL, and UNIQUE for correct constraints [OK]

Common Mistakes:

• Forgetting NOT NULL on required columns
• Using INT without SERIAL for auto-increment
• Missing UNIQUE constraint on email