UNIQUE constraint in SQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add a UNIQUE constraint on the email column.

SQL

CREATE TABLE users (id INT PRIMARY KEY, email VARCHAR(255) [1]);

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AUNIQUE

BPRIMARY KEY

CNOT NULL

DCHECK

Attempts:

3 left

💡 Hint

Common Mistakes

Using PRIMARY KEY instead of UNIQUE for email column.

Forgetting to add any constraint, allowing duplicates.

The UNIQUE constraint ensures that all values in the email column are different.

2fill in blank

easy

Complete the code to add a UNIQUE constraint on the code column.

SQL

CREATE TABLE products (id INT PRIMARY KEY, code VARCHAR(50) [1]);

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

ACHECK

BUNIQUE

CPRIMARY KEY

DNOT NULL

Attempts:

3 left

💡 Hint

Common Mistakes

Using PRIMARY KEY instead of UNIQUE for code column.

Forgetting to add any constraint, allowing duplicates.

The UNIQUE constraint ensures that all values in the code column are different.

3fill in blank

medium

Complete the code to add a UNIQUE constraint to the username column after table creation.

SQL

ALTER TABLE users ADD CONSTRAINT [1] UNIQUE (username);

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Aunique_username

Bcheck_username

Cpk_username

Dfk_username

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'pk_' prefix which is for primary keys.

Using 'fk_' which is for foreign keys.

You must name the UNIQUE constraint. 'unique_username' is a good descriptive name.

4fill in blank

hard

Fill both blanks to create a UNIQUE constraint on two columns: first_name and last_name.

SQL

ALTER TABLE employees ADD CONSTRAINT [1] [2] (first_name, last_name);

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Aunique_fullname

BPRIMARY KEY

CUNIQUE

DCHECK

Attempts:

3 left

💡 Hint

Common Mistakes

Using PRIMARY KEY instead of UNIQUE for multiple columns.

Not naming the constraint.

The constraint name is 'unique_fullname' and the type is UNIQUE to ensure the combination of first_name and last_name is unique.

5fill in blank

hard

Fill all three blanks to create a table with a UNIQUE constraint on the email column and a PRIMARY KEY on id.

SQL

CREATE TABLE customers ([1] INT [2], email VARCHAR(255) [3]);

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

Aid

BPRIMARY KEY

CUNIQUE

DNOT NULL

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to add PRIMARY KEY to id.

Not adding UNIQUE to email.

The id column is defined as PRIMARY KEY, and the email column has a UNIQUE constraint to prevent duplicate emails.