Sparse index pattern in DynamoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Querying a sparse index for items with a specific attribute

You have a DynamoDB table with a sparse global secondary index (GSI) on attribute status. Only items with status set appear in the index.

What will the following query on the GSI return?

Query on GSI where status = 'active'

A Items without the status attribute will be returned.

B All items in the table will be returned regardless of status.

C Only items where the attribute status equals 'active' will be returned.

D The query will return an error because status is not a primary key.

💡 Hint

Remember, a sparse index only contains items where the indexed attribute exists.

A sparse index in DynamoDB only includes items that have the indexed attribute. Querying the GSI with status = 'active' returns only those items with that status.

🧠 Conceptual

intermediate

Why use a sparse index in DynamoDB?

What is the main advantage of using a sparse index in DynamoDB?

A It reduces storage and query costs by indexing only a subset of items.

B It automatically backs up all table data.

C It speeds up writes by indexing every attribute.

D It encrypts data stored in the index.

💡 Hint

Think about what happens when only some items have the indexed attribute.

Sparse indexes only include items with the indexed attribute, so they are smaller and cheaper to query than full indexes.

📝 Syntax

advanced

Identify the correct DynamoDB GSI definition for a sparse index

Which of the following GSI definitions correctly creates a sparse index on attribute category?

A { "IndexName": "CategoryIndex", "KeySchema": [{"AttributeName": "category", "KeyType": "HASH"}], "Projection": {"ProjectionType": "ALL"} }

B { "IndexName": "CategoryIndex", "KeySchema": [{"AttributeName": "category", "KeyType": "HASH"}], "Projection": {"ProjectionType": "INCLUDE", "NonKeyAttributes": ["price"]} }

C { "IndexName": "CategoryIndex", "KeySchema": [{"AttributeName": "category", "KeyType": "HASH"}], "Projection": {"ProjectionType": "KEYS_ONLY"} }

D { "IndexName": "CategoryIndex", "KeySchema": [{"AttributeName": "category", "KeyType": "RANGE"}], "Projection": {"ProjectionType": "ALL"} }

💡 Hint

A sparse index requires the indexed attribute as the partition key (HASH).

To create a sparse index, the GSI must have the attribute as the HASH key. Option A correctly sets category as HASH key with full projection.

❓ optimization

advanced

Optimizing queries using sparse indexes

You want to efficiently query only items with a priority attribute set to 'high'. Which approach best uses a sparse index?

A Scan the entire table and filter items where <code>priority</code> = 'high'.

B Create a GSI with <code>priority</code> as a sort key and query all items filtering by 'high'.

C Create a local secondary index on <code>priority</code> without changing the table schema.

D Create a GSI with <code>priority</code> as the partition key and only items with <code>priority</code> set will appear in the index.

💡 Hint

Sparse indexes only include items with the indexed attribute as partition key.

Using priority as the partition key in a GSI creates a sparse index that contains only items with that attribute, making queries efficient.

🔧 Debug

expert

Why does querying a sparse index return no results?

You created a sparse GSI on attribute region. You query the GSI for region = 'us-east-1' but get no results, even though items with that region exist in the table.

What is the most likely cause?

A Sparse indexes do not support querying by partition key.

B The items with region 'us-east-1' do not have the region attribute set exactly as the GSI expects.

C The table does not have any items with region attribute at all.

D The GSI was created with region as a sort key instead of partition key.

💡 Hint

Check if the attribute values exactly match the GSI key attribute.

If the attribute values differ in case or type, or are missing, the sparse index will not include those items, causing queries to return no results.