Primary vs secondary indexes in DBMS Theory - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to identify the type of index that uniquely identifies each record in a database table.

DBMS Theory

The index that uniquely identifies each record is called a [1] index.

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

Aclustered

Bsecondary

Cforeign

Dprimary

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing primary index with secondary index.

Thinking foreign key is an index type.

A primary index uniquely identifies each record in a database table. It ensures that no two rows have the same key value.

2fill in blank

medium

Complete the sentence to describe the index used to improve query performance on non-primary key columns.

DBMS Theory

An index created on columns other than the primary key to speed up queries is called a [1] index.

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

Aprimary

Bsecondary

Cunique

Dclustered

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing secondary index with primary index.

Assuming secondary index enforces uniqueness.

A secondary index is created on columns other than the primary key to improve query speed. It does not guarantee uniqueness.

3fill in blank

hard

Fix the error in the statement about primary indexes.

DBMS Theory

A primary index [1] allow duplicate key values.

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Acannot

Bshould

Ccan

Dmay

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing 'can' or 'may' which imply duplicates are allowed.

Confusing primary index rules with secondary index rules.

A primary index cannot allow duplicate key values because it uniquely identifies each record.

4fill in blank

hard

Fill both blanks to complete the description of secondary indexes.

DBMS Theory

Secondary indexes [1] the primary index and [2] the uniqueness enforced by the primary index.

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Aare separate from

Bare the same as

Cdo not affect

Dalways replace

Attempts:

3 left

💡 Hint

Common Mistakes

Thinking secondary indexes replace the primary index.

Assuming secondary indexes enforce uniqueness.

Secondary indexes are separate from the primary index and do not affect the uniqueness enforced by the primary index. They help improve query speed on columns other than the primary key.

5fill in blank

hard

Fill all three blanks to complete the dictionary that creates a mapping of index types to their main characteristics.

DBMS Theory

index_info = { [1]: '[2]', '[3]': 'Improves query speed on non-key columns'}

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A'Primary Index'

BPrimary Index

CSecondary Index

DUniqueness enforced

Attempts:

3 left

💡 Hint

Common Mistakes

Not using curly braces for dictionary.

Mixing up keys and values.

Forgetting quotes around string keys.

The dictionary index_info maps Primary Index to 'Uniqueness enforced' and Secondary Index to 'Improves query speed on non-key columns'.

Practice

1. What is the main purpose of a primary index in a database?

easy

A. To provide unique and fast access to records using the primary key

B. To speed up searches on non-key columns

C. To store duplicate values for faster retrieval

D. To backup the database automatically

Solution

1. Step 1: Understand the role of primary index

   A primary index is created on the primary key of a table, which uniquely identifies each record.

2. Step 2: Identify its main function

   It ensures fast and unique access to records based on the primary key values.

3. Final Answer:

   To provide unique and fast access to records using the primary key -> Option A

4. Quick Check:

   Primary index = unique fast access [OK]

Hint: Primary index = unique key fast access [OK]

Common Mistakes:

• Confusing primary index with secondary index
• Thinking primary index allows duplicates
• Assuming primary index is for backup

2. Which of the following is the correct statement about creating a secondary index in SQL?

easy

A. CREATE INDEX idx_name ON table(column);

B. CREATE UNIQUE INDEX idx_name ON table(column);

C. CREATE PRIMARY INDEX idx_name ON table(column);

D. CREATE SECONDARY INDEX idx_name ON table(column);

Solution

1. Step 1: Recall SQL syntax for indexes

   Secondary indexes are created using the standard CREATE INDEX statement without the PRIMARY keyword.

2. Step 2: Identify the correct syntax

   CREATE INDEX idx_name ON table(column); uses the correct syntax: CREATE INDEX idx_name ON table(column);

3. Final Answer:

   CREATE INDEX idx_name ON table(column); -> Option A

4. Quick Check:

   Secondary index syntax = CREATE INDEX [OK]

Hint: Secondary index uses CREATE INDEX without PRIMARY [OK]

Common Mistakes:

• Using CREATE SECONDARY INDEX which is invalid
• Confusing with CREATE PRIMARY INDEX syntax
• Using UNIQUE keyword incorrectly for secondary index

3. Consider a table Employees(emp_id, name, department) where emp_id is the primary key. Which index type would speed up a query filtering by department?

medium

A. Primary index on department

B. Primary index on emp_id

C. Secondary index on department

D. No index needed

Solution

1. Step 1: Identify the primary key and its index

   The primary key is emp_id, so the primary index is on emp_id.

2. Step 2: Determine which index helps filter by department

   Since department is not the primary key, a secondary index on department speeds up queries filtering by it.

3. Final Answer:

   Secondary index on department -> Option C

4. Quick Check:

   Filter by non-key column = secondary index [OK]

Hint: Use secondary index for non-primary key columns [OK]

Common Mistakes:

• Assuming primary index helps filter by any column
• Trying to create primary index on non-key column
• Ignoring the benefit of secondary indexes

4. A developer created a secondary index on a column that contains many duplicate values. What is the likely problem?

medium

A. The database will reject the index creation

B. The primary index will be corrupted

C. The secondary index will enforce uniqueness

D. The secondary index will be inefficient due to low uniqueness

Solution

1. Step 1: Understand secondary index behavior with duplicates

   Secondary indexes can be created on columns with duplicates but may become less efficient because many records share the same key.

2. Step 2: Identify the impact on performance

   Low uniqueness means the index has many entries pointing to multiple rows, slowing down search performance.

3. Final Answer:

   The secondary index will be inefficient due to low uniqueness -> Option D

4. Quick Check:

   Duplicates in secondary index = inefficiency [OK]

Hint: Secondary index on duplicates slows searches [OK]

Common Mistakes:

• Thinking secondary index enforces uniqueness
• Believing primary index gets corrupted
• Expecting index creation to fail

5. You have a large table with a primary index on customer_id and a secondary index on city. You want to optimize queries filtering by both customer_id and city. What is the best indexing strategy?

hard

A. Drop the secondary index and rely only on primary index

B. Create a composite index on (customer_id, city)

C. Create a secondary index on customer_id only

D. Create two separate secondary indexes on customer_id and city

Solution

1. Step 1: Analyze current indexes and query filters

   Primary index exists on customer_id, secondary index on city. Queries filter by both columns.

2. Step 2: Understand composite index benefits

   A composite index on (customer_id, city) allows efficient filtering on both columns together, improving query speed.

3. Step 3: Evaluate other options

   Dropping indexes or creating separate secondary indexes won't optimize combined filtering as well as a composite index.

4. Final Answer:

   Create a composite index on (customer_id, city) -> Option B

5. Quick Check:

   Combined filter = composite index [OK]

Hint: Use composite index for multi-column filters [OK]

Common Mistakes:

• Dropping useful indexes
• Creating redundant secondary indexes
• Ignoring composite index advantages