B-tree index (default) behavior in PostgreSQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a B-tree index on the column 'username' in the 'users' table.

PostgreSQL

CREATE INDEX idx_username ON users ([1]);

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

Aemail

Buser_id

Cusername

Dcreated_at

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing a column not related to the query filter.

Using a column that does not exist in the table.

The B-tree index is created on the 'username' column to speed up queries filtering by username.

2fill in blank

medium

Complete the code to create a B-tree index that sorts the 'created_at' column in descending order.

PostgreSQL

CREATE INDEX idx_created_desc ON orders ([1] DESC);

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

Aorder_id

Bcreated_at

Ccustomer_id

Dstatus

Attempts:

3 left

💡 Hint

Common Mistakes

Using a column unrelated to date or time.

Forgetting to specify DESC for descending order.

The index is created on 'created_at' column with descending order to optimize queries sorting by newest orders first.

3fill in blank

hard

Fix the error in the index creation statement to use the default B-tree index on the 'email' column.

PostgreSQL

CREATE INDEX idx_email ON customers ([1]);

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

Aemail

Bemail DESC

Cemail ASC NULLS LAST

Demail NULLS FIRST

Attempts:

3 left

💡 Hint

Common Mistakes

Adding DESC or NULLS clauses unnecessarily.

Using unsupported syntax for B-tree index.

Using just the column name 'email' creates a default B-tree index with ascending order and default NULLS placement.

4fill in blank

hard

Fill both blanks to create a B-tree index on 'last_name' and 'first_name' columns for sorting by last name ascending and first name descending.

PostgreSQL

CREATE INDEX idx_name ON employees ([1] ASC, [2] DESC);

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

Alast_name

Bfirst_name

Cmiddle_name

Demployee_id

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the order of columns.

Using unrelated columns for the index.

The index sorts by 'last_name' ascending and 'first_name' descending to optimize queries ordering by full name.

5fill in blank

hard

Fill all three blanks to create a B-tree index on 'category', 'price' ascending, and 'stock' descending columns.

PostgreSQL

CREATE INDEX idx_product ON products ([1], [2] ASC, [3] DESC);

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

Acategory

Bprice

Cstock

Dproduct_id

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up the order or sort directions.

Including unrelated columns.

This index helps queries filtering by category and sorting by price ascending and stock descending.

Practice

1. What is the primary purpose of a B-tree index in PostgreSQL?

easy

A. To speed up searching and sorting operations

B. To store large binary objects

C. To manage user permissions

D. To backup the database automatically

Solution

1. Step 1: Understand the role of indexes

   Indexes help databases find data faster without scanning the entire table.

2. Step 2: Identify B-tree index function

   B-tree indexes organize data to speed up searching and sorting efficiently.

3. Final Answer:

   To speed up searching and sorting operations -> Option A

4. Quick Check:

   B-tree index = speed up search/sort [OK]

Hint: B-tree indexes speed up search and sort operations [OK]

Common Mistakes:

• Confusing B-tree with storing large objects
• Thinking indexes manage permissions
• Assuming indexes handle backups

2. Which of the following is the correct syntax to create a B-tree index on the column username of table users?

easy

A. CREATE BTREE INDEX idx_username ON users (username);

B. CREATE INDEX idx_username ON users USING bitmap (username);

C. CREATE INDEX idx_username ON users (username) USING hash;

D. CREATE INDEX idx_username ON users USING btree (username);

Solution

1. Step 1: Recall correct CREATE INDEX syntax

   The syntax is CREATE INDEX index_name ON table_name USING index_type (column);

2. Step 2: Identify correct index type and syntax

   B-tree is default and specified as USING btree; CREATE INDEX idx_username ON users USING btree (username); matches this exactly.

3. Final Answer:

   CREATE INDEX idx_username ON users USING btree (username); -> Option D

4. Quick Check:

   Correct syntax uses USING btree [OK]

Hint: Use 'USING btree' in CREATE INDEX for B-tree indexes [OK]

Common Mistakes:

• Using incorrect index type like hash or bitmap
• Wrong keyword order in CREATE INDEX
• Omitting USING clause or misspelling it

3. Given a table products(id SERIAL PRIMARY KEY, price NUMERIC) with a B-tree index on price, what will the query SELECT * FROM products WHERE price > 100 ORDER BY price; most likely use?

medium

A. A sequential scan ignoring the index

B. A B-tree index scan to quickly find rows with price > 100

C. A hash index scan on price

D. A bitmap index scan on price

Solution

1. Step 1: Understand query conditions and index type

   The query filters with price > 100 and orders by price; B-tree indexes support range queries and sorting.

2. Step 2: Identify index usage

   PostgreSQL will use the B-tree index to efficiently find and order matching rows.

3. Final Answer:

   A B-tree index scan to quickly find rows with price > 100 -> Option B

4. Quick Check:

   Range query + order = B-tree index scan [OK]

Hint: Range queries with ORDER BY use B-tree index scans [OK]

Common Mistakes:

• Assuming sequential scan always used
• Confusing hash or bitmap index usage
• Ignoring index benefits for range queries

4. You created a B-tree index on column email but notice queries filtering by LOWER(email) are slow. What is the likely problem?

medium

A. B-tree indexes only work on numeric columns

B. The index was created on the wrong table

C. B-tree indexes do not support functions like LOWER() by default

D. The database needs to be restarted to use the index

Solution

1. Step 1: Understand function usage in WHERE clause

   Using LOWER(email) means the query filters on a transformed value, not the raw column.

2. Step 2: Recognize index limitations

   Regular B-tree indexes do not support functions unless a functional index is created.

3. Final Answer:

   B-tree indexes do not support functions like LOWER() by default -> Option C

4. Quick Check:

   Function in filter needs functional index [OK]

Hint: Use functional indexes for queries with functions like LOWER() [OK]

Common Mistakes:

• Thinking B-tree only works on numbers
• Assuming index applies automatically after restart
• Mistaking wrong table for index issue

5. You want to enforce uniqueness on a column serial_number and speed up queries filtering by it. Which is the best approach using B-tree indexes?

hard

A. Create a UNIQUE B-tree index on serial_number

B. Create a non-unique B-tree index and a separate UNIQUE constraint

C. Create a hash index and a UNIQUE constraint

D. Create a UNIQUE constraint without an index

Solution

1. Step 1: Understand uniqueness enforcement

   PostgreSQL enforces UNIQUE constraints using unique indexes, usually B-tree by default.

2. Step 2: Combine uniqueness and performance

   Creating a UNIQUE B-tree index both enforces uniqueness and speeds up lookups on that column.

3. Final Answer:

   Create a UNIQUE B-tree index on serial_number -> Option A

4. Quick Check:

   Unique B-tree index = uniqueness + speed [OK]

Hint: Use UNIQUE B-tree index to enforce uniqueness and speed queries [OK]

Common Mistakes:

• Creating separate index and constraint unnecessarily
• Using hash index which doesn't enforce uniqueness
• Assuming UNIQUE constraint works without an index