Single column index in SQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a single column index on the 'name' column of the 'employees' table.

SQL

CREATE INDEX [1] ON employees(name);

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

Aname_index

Bindex_name

Cidx_name

Didx_employees

Attempts:

3 left

💡 Hint

Common Mistakes

Using reserved keywords as index names.

Omitting the index name entirely.

The index name can be any valid identifier. Here, idx_name is a common naming style for indexes on the 'name' column.

2fill in blank

medium

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

SQL

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

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

AUNIQUE

BFOREIGN

CPRIMARY

DFULLTEXT

Attempts:

3 left

💡 Hint

Common Mistakes

Using PRIMARY instead of UNIQUE for a unique index.

Confusing FULLTEXT with UNIQUE.

The UNIQUE keyword ensures that all values in the 'email' column are distinct.

3fill in blank

hard

Fix the error in the code to create an index on the 'date' column of the 'orders' table.

SQL

CREATE INDEX idx_date ON orders([1]);

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

Adate

BorderDate

Cdates

Dorder_date

Attempts:

3 left

💡 Hint

Common Mistakes

Using a plural form of the column name.

Using a different column name that does not exist.

The column name must exactly match the existing column in the table. Here, the column is named date.

4fill in blank

hard

Fill both blanks to create a unique index named 'idx_user_id' on the 'user_id' column of the 'sessions' table.

SQL

CREATE [1] INDEX [2] ON sessions(user_id);

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

AUNIQUE

Bidx_sessions

Cidx_user_id

DINDEX

Attempts:

3 left

💡 Hint

Common Mistakes

Using a non-unique keyword for a unique index.

Using a wrong index name.

The UNIQUE keyword creates a unique index, and the index name should be idx_user_id as specified.

5fill in blank

hard

Fill all three blanks to create a single column index named 'idx_product_code' on the 'code' column of the 'products' table with the index type 'BTREE'.

SQL

CREATE [1] INDEX [2] ON products([3]) USING BTREE;

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

AINDEX

Bidx_product_code

Ccode

DUNIQUE

Attempts:

3 left

💡 Hint

Common Mistakes

Using UNIQUE instead of INDEX for a normal index.

Using wrong column or index names.

The keyword INDEX creates a normal index, the name is idx_product_code, and the column is code. The USING BTREE specifies the index type.

Practice

1.

What is the main purpose of creating a single column index in a database?

easy

A. To store duplicate values in the column

B. To automatically backup the database

C. To prevent any changes to the column data

D. To speed up queries that filter or sort by that column

Solution

1. Step 1: Understand what an index does

   An index helps the database find rows faster when searching or sorting by the indexed column.

2. Step 2: Identify the purpose of a single column index

   A single column index speeds up queries that use that column in WHERE or ORDER BY clauses.

3. Final Answer:

   To speed up queries that filter or sort by that column -> Option D

4. Quick Check:

   Index speeds up queries = B [OK]

Hint: Index speeds up searches on one column [OK]

Common Mistakes:

• Thinking index stores duplicate values
• Believing index prevents data changes
• Confusing index with backup

2.

Which of the following is the correct syntax to create a single column index on the email column of a table named users?

easy

A. CREATE INDEX users ON idx_email(email);

B. CREATE INDEX idx_email ON users(email);

C. CREATE INDEX email ON users idx_email;

D. CREATE users INDEX idx_email(email);

Solution

1. Step 1: Recall the syntax for creating an index

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

2. Step 2: Match the syntax with the options

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

3. Final Answer:

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

4. Quick Check:

   CREATE INDEX index_name ON table(column) = A [OK]

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

Common Mistakes:

• Swapping table and index names
• Missing ON keyword
• Incorrect order of keywords

3.

Given a table products with columns id, name, and category, and a single column index on category, what will the query below most likely do?

SELECT * FROM products WHERE category = 'Books';

medium

A. Use the index to quickly find rows where category is 'Books'

B. Sort the results by category before returning

C. Return an error because index cannot be used in WHERE clause

D. Scan the entire table without using the index

Solution

1. Step 1: Understand how an index affects a WHERE query

   An index on the category column helps the database quickly locate rows matching the condition category = 'Books'.

2. Step 2: Analyze the query behavior with the index

   The query will use the index to avoid scanning the whole table, speeding up the search.

3. Final Answer:

   Use the index to quickly find rows where category is 'Books' -> Option A

4. Quick Check:

   Index speeds WHERE search = D [OK]

Hint: WHERE on indexed column uses index for speed [OK]

Common Mistakes:

• Assuming index is ignored in WHERE clause
• Thinking index causes errors in queries
• Confusing index use with sorting

4.

Consider this SQL statement to create an index:

CREATE INDEX idx_price ON products price;

What is wrong with this statement?

medium

A. Table name should come after the column name

B. Index name cannot start with 'idx_'

C. Missing parentheses around the column name

D. CREATE INDEX cannot be used on numeric columns

Solution

1. Step 1: Check the syntax for CREATE INDEX

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

2. Step 2: Identify the syntax error

   The statement is missing parentheses around price. It should be ON products(price).

3. Final Answer:

   Missing parentheses around the column name -> Option C

4. Quick Check:

   Column name needs parentheses = C [OK]

Hint: Column name must be in parentheses after table [OK]

Common Mistakes:

• Omitting parentheses around column
• Misplacing table and column names
• Thinking index names have restrictions

5.

You have a table orders with columns order_id, customer_id, and order_date. You want to speed up queries that filter by customer_id and sort by order_date. Which approach is best?

hard

A. Create a composite index on customer_id and order_date

B. Create a single column index on order_date only

C. Create a single column index on customer_id only

D. Create no index to avoid slowing down inserts

Solution

1. Step 1: Understand query needs

   Queries filter by customer_id and sort by order_date, so both columns matter.

2. Step 2: Choose the best index type

   A composite index on both columns helps filter and sort efficiently, better than single column indexes.

3. Final Answer:

   Create a composite index on customer_id and order_date -> Option A

4. Quick Check:

   Composite index for filter + sort = A [OK]

Hint: Use composite index for multiple column queries [OK]

Common Mistakes:

• Using single column index when composite is better
• Avoiding indexes fearing insert slowdown
• Indexing only sort column ignoring filter