Unique indexes in MySQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a unique index on the column 'email' in the 'users' table.

MySQL

CREATE UNIQUE INDEX [1] ON users(email);

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

Aidx_users_email

Bidx_email_unique

Cemail_index

Dunique_email

Attempts:

3 left

💡 Hint

Common Mistakes

Using a name that is already used by another index.

Forgetting to specify UNIQUE keyword (though here it's part of the statement).

The index name can be any valid identifier. Here, idx_email_unique clearly indicates a unique index on the email column.

2fill in blank

medium

Complete the code to add a unique constraint on the 'username' column in the 'accounts' table.

MySQL

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

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Ausername_unique

Busername_key

Cunique_username

Dunique_key

Attempts:

3 left

💡 Hint

Common Mistakes

Using a generic name like 'unique_key' which is not descriptive.

Using a name that conflicts with existing constraints.

The constraint name username_unique clearly indicates a unique constraint on the username column.

3fill in blank

hard

Fix the error in the code to create a unique index on 'phone_number' in the 'contacts' table.

MySQL

CREATE [1] INDEX idx_phone ON contacts(phone_number);

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AFULLTEXT

BPRIMARY

CFOREIGN

DUNIQUE

Attempts:

3 left

💡 Hint

Common Mistakes

Using PRIMARY or FOREIGN which are for different constraints.

Omitting the UNIQUE keyword.

The keyword UNIQUE is required to create a unique index. Other options are for different index types.

4fill in blank

hard

Fill both blanks to create a unique index named 'idx_unique_code' on the 'code' column of the 'products' table.

MySQL

CREATE [1] INDEX [2] ON products(code);

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AUNIQUE

Bidx_code

Cidx_unique_code

DPRIMARY

Attempts:

3 left

💡 Hint

Common Mistakes

Using PRIMARY instead of UNIQUE.

Using a different index name than requested.

The keyword UNIQUE creates a unique index, and the index name should be idx_unique_code as requested.

5fill in blank

hard

Fill all three blanks to add a unique constraint named 'uc_email' on the 'email' column of the 'subscribers' table.

MySQL

ALTER TABLE [1] ADD CONSTRAINT [2] [3] (email);

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

Asubscribers

Buc_email

CUNIQUE

Dusers

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong table name.

Using a generic constraint name.

Omitting the UNIQUE keyword.

The table is subscribers, the constraint name is uc_email, and the keyword UNIQUE enforces uniqueness.