Basic scan operation in DynamoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What does this DynamoDB scan return?

Consider a DynamoDB table named Books with items having attributes Title and Author. The following scan operation is executed:

ScanInput = { TableName: "Books" }

What will be the output of this scan?

DynamoDB

const params = { TableName: "Books" };
const result = await dynamodb.scan(params).promise();
return result.Items;

A Only the first 10 items are returned by default.

B Only items with attribute Author = 'Unknown' are returned.

C No items are returned because no filter is specified.

D All items in the Books table are returned.

💡 Hint

A scan without filters returns all items in the table.

A scan operation without any filter or limit returns all items in the table. It reads every item and returns them.

❓ query_result

intermediate

What is the output of this filtered scan?

Given a DynamoDB table Users with attribute Age, the following scan is run:

ScanInput = {
  TableName: "Users",
  FilterExpression: "Age > :minAge",
  ExpressionAttributeValues: { ":minAge": 30 }
}

What does this scan return?

DynamoDB

const params = {
  TableName: "Users",
  FilterExpression: "Age > :minAge",
  ExpressionAttributeValues: { ":minAge": 30 }
};
const result = await dynamodb.scan(params).promise();
return result.Items;

A All users with Age greater than 30 are returned.

B All users are returned because FilterExpression is ignored in scan.

C Only users with Age exactly 30 are returned.

D Scan returns an error due to invalid FilterExpression syntax.

💡 Hint

FilterExpression filters items after scanning all.

FilterExpression filters the scanned items to only those matching the condition. Here, only users with Age > 30 are returned.

📝 Syntax

advanced

Which scan parameter causes a syntax error?

Identify which of the following scan parameter objects will cause a syntax error when used in DynamoDB scan operation.

A { TableName: "Orders", FilterExpression: "Price > :p", ExpressionAttributeValues: { ":p": 100 } }

B { TableName: "Orders", FilterExpression: "Price > :p", ExpressionAttributeValues: { ":p" 100 } }

C { TableName: "Orders", Limit: 5 }

D { TableName: "Orders" }

💡 Hint

Check for missing colon or comma in object literals.

Option B is missing a colon between ":p" and 100 in ExpressionAttributeValues, causing a syntax error.

❓ optimization

advanced

How to optimize a scan to reduce read capacity usage?

You want to scan a large DynamoDB table but reduce the read capacity units consumed. Which option below helps achieve this?

A Use FilterExpression to reduce items scanned.

B Use ScanIndexForward to scan in ascending order.

C Use ProjectionExpression to return only needed attributes.

D Use ConsistentRead set to true.

💡 Hint

Returning fewer attributes reduces data read.

ProjectionExpression limits attributes returned, reducing data size and read capacity used. FilterExpression filters after reading all items, so it doesn't reduce read capacity.

🔧 Debug

expert

Why does this scan return fewer items than expected?

A DynamoDB scan on table Products uses the following parameters:

{ TableName: "Products", Limit: 5 }

After running the scan, only 3 items are returned, but the table has 10 items. Why?

A Scan Limit limits the number of items returned, but if FilterExpression excludes some items, fewer are returned.

B Scan Limit limits the number of items returned, but scan may return fewer if fewer items are available in the segment.

C Scan Limit limits the number of items returned, but scan may return fewer if the response is paginated and only first page is fetched.

D Scan Limit limits the number of items evaluated, not the number returned after filtering.

💡 Hint

Consider if any filtering is applied after scan.

If a FilterExpression is used, the Limit applies before filtering, so fewer items may be returned after filtering excludes some items.