Creating indexes in MySQL - Try It Yourself

Creating Indexes in MySQL

📖 Scenario: You are managing a small online bookstore database. The books table stores information about each book, including its id, title, and author. To help the database find books faster when searching by title, you want to create an index on the title column.

🎯 Goal: Build a MySQL script that creates a books table and then adds an index on the title column to speed up searches.

📋 What You'll Learn

Create a books table with columns id (integer primary key), title (varchar 100), and author (varchar 100).

Add an index named idx_title on the title column.

Use standard MySQL syntax for table creation and index creation.

💡 Why This Matters

🌍 Real World

Indexes help databases find data faster, which is important for websites and apps that need quick responses.

💼 Career

Database administrators and backend developers often create and manage indexes to improve application performance.

1

Create the books table

Write a MySQL statement to create a table called books with three columns: id as an integer primary key, title as a varchar(100), and author as a varchar(100).

MySQL

-- Create the books table with id, title, and author columns
-- Your code here

Hint

Use CREATE TABLE books (id INT PRIMARY KEY, title VARCHAR(100), author VARCHAR(100));

2

Prepare to add an index

Add a comment line that says -- Prepare to add index on title to your script after the table creation statement.

MySQL

CREATE TABLE books (
  id INT PRIMARY KEY,
  title VARCHAR(100),
  author VARCHAR(100)
);
-- Prepare to add index on title
-- Your code here

Hint

Just add a comment line exactly as shown.

3

Create an index on the title column

Write a MySQL statement to create an index named idx_title on the title column of the books table.

MySQL

CREATE TABLE books (
  id INT PRIMARY KEY,
  title VARCHAR(100),
  author VARCHAR(100)
);
-- Prepare to add index on title
CREATE INDEX idx_title ON books(title);
-- Your code here

Hint

Use CREATE INDEX idx_title ON books(title); to add the index.

4

Complete the script with a comment

Add a comment line at the end of the script that says -- Index created successfully.

MySQL

CREATE TABLE books (
  id INT PRIMARY KEY,
  title VARCHAR(100),
  author VARCHAR(100)
);
-- Prepare to add index on title
CREATE INDEX idx_title ON books(title);
-- Index created successfully
-- Your code here

Hint

Just add the comment line exactly as shown.

Practice

1. What is the main purpose of creating an index on a column in a MySQL table?

easy

A. To speed up data retrieval when searching or filtering

B. To store duplicate values in the column

C. To increase the size of the database

D. To automatically backup the table data

Solution

1. Step 1: Understand what an index does

   An index acts like a shortcut to find data faster in a table.

2. Step 2: Identify the main benefit

   Indexes speed up searches and filtering by avoiding full table scans.

3. Final Answer:

   To speed up data retrieval when searching or filtering -> Option A

4. Quick Check:

   Index = faster search [OK]

Hint: Indexes speed up searches by creating shortcuts [OK]

Common Mistakes:

• Thinking indexes store duplicate values
• Believing indexes increase database size significantly
• Confusing indexes with backups

2. Which of the following is the correct syntax to create a simple index on the column email in a table named users?

easy

A. INDEX CREATE email_index ON users (email);

B. CREATE INDEX email_index ON users (email);

C. CREATE INDEX users.email_index (email);

D. CREATE INDEX ON users email_index (email);

Solution

1. Step 1: Recall MySQL index creation syntax

   The correct syntax is: CREATE INDEX index_name ON table_name (column_name);

2. Step 2: Match the syntax with options

   CREATE INDEX email_index ON users (email); matches the correct syntax exactly.

3. Final Answer:

   CREATE INDEX email_index ON users (email); -> Option B

4. Quick Check:

   CREATE INDEX index_name ON table (column) [OK]

Hint: Syntax: CREATE INDEX name ON table (column) [OK]

Common Mistakes:

• Swapping order of table and index name
• Omitting ON keyword
• Using wrong keyword order

3. Given the table products with columns id, name, and category, what will be the effect of this query?

CREATE UNIQUE INDEX idx_name ON products (name);

medium

A. It allows duplicate product names in the table

B. It creates a backup of the products table

C. It deletes rows with duplicate names

D. It prevents duplicate product names and speeds up searches by name

Solution

1. Step 1: Understand UNIQUE index effect

   A UNIQUE index prevents duplicate values in the indexed column.

2. Step 2: Identify additional benefit

   Indexes also speed up searches on that column.

3. Final Answer:

   It prevents duplicate product names and speeds up searches by name -> Option D

4. Quick Check:

   UNIQUE index = no duplicates + faster search [OK]

Hint: UNIQUE index blocks duplicates and speeds search [OK]

Common Mistakes:

• Thinking UNIQUE index allows duplicates
• Confusing index with backup or delete
• Ignoring speed improvement

4. You try to create an index with this command:

CREATE INDEX idx_age ON employees age;

What is the error in this statement?

medium

A. Table name is missing

B. Index name cannot start with 'idx_'

C. Missing parentheses around the column name

D. Cannot create index on numeric columns

Solution

1. Step 1: Check syntax for CREATE INDEX

   The column list must be inside parentheses after the table name.

2. Step 2: Identify the error

   The statement lacks parentheses around age, causing syntax error.

3. Final Answer:

   Missing parentheses around the column name -> Option C

4. Quick Check:

   Columns must be in parentheses [OK]

Hint: Always put columns in parentheses after table name [OK]

Common Mistakes:

• Forgetting parentheses around columns
• Thinking index names have restrictions
• Assuming numeric columns can't be indexed

5. You have a large orders table with columns order_id, customer_id, and order_date. You often query orders by customer_id and order_date. Which index creation will best improve query speed without allowing duplicate entries for the same customer on the same date?

hard

A. CREATE UNIQUE INDEX idx_customer_date ON orders (customer_id, order_date);

B. CREATE INDEX idx_customer ON orders (customer_id);

C. CREATE INDEX idx_order_date ON orders (order_date);

D. CREATE UNIQUE INDEX idx_order_id ON orders (order_id);

Solution

1. Step 1: Analyze query needs

   Queries filter by both customer_id and order_date, so a composite index on both is best.

2. Step 2: Consider uniqueness requirement

   To prevent duplicate orders for the same customer on the same date, use a UNIQUE index on both columns.

3. Final Answer:

   CREATE UNIQUE INDEX idx_customer_date ON orders (customer_id, order_date); -> Option A

4. Quick Check:

   Composite UNIQUE index matches query and uniqueness [OK]

Hint: Use composite UNIQUE index for multi-column uniqueness and speed [OK]

Common Mistakes:

• Creating single-column indexes only
• Ignoring uniqueness requirement
• Indexing unrelated columns