AWS DVA-C02 Drill: DynamoDB Query Sorting - ScanIndexForward Flag Explained

Jeff’s Note

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Unlike generic exam dumps, ADH analyzes this scenario through the lens of a Real-World Lead Developer.

For DVA-C02 candidates, the confusion often lies in how to control query result order in DynamoDB. In production, this is about knowing exactly which API parameter governs ascending vs. descending sort order for Query operations. Let’s drill down.

The Certification Drill (Simulated Question)

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Scenario

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In a fintech startup called FinSight, a backend developer has implemented a DynamoDB table to store transaction orders. The table uses TransactionID as the partition key and ItemsCount as the sort key, both numbers. By default, when the developer queries this table by TransactionID, the results are sorted in ascending order by ItemsCount.

The Requirement:

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The developer wants the query results sorted in descending order by ItemsCount, so that transactions with more items appear first.

The Options

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• A) Create a local secondary index (LSI) on the ItemsCount sort key.
• B) Change the sort key from ItemsCount to ItemsCountDescending.
• C) In the Query operation, set the ScanIndexForward parameter to false.
• D) In the Query operation, set the KeyConditionExpression parameter to false.

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Correct Answer

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C) In the Query operation, set the ScanIndexForward parameter to false.

Quick Insight: The Developer Imperative

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The ScanIndexForward boolean parameter controls whether results are returned in ascending (true) or descending (false) order according to the sort key in a Query call. Setting it to false reverses the default ascending order without needing table schema changes or new indexes.

Content Locked: The Expert Analysis

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You’ve identified the answer. But do you know the implementation details that separate a Junior from a Senior?

The Expert’s Analysis

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Correct Answer

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Option C

The Winning Logic

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DynamoDB Query API supports a parameter called ScanIndexForward. By default, it is true, which returns results sorted in ascending order by the sort key (ItemsCount in this case).
To get descending order results, simply set ScanIndexForward to false during the query operation—no need to alter key definitions or create indexes. The sort key stays the same, but the results are reversed at query time. This enables dynamic ordering without changing table schema or indexes.

The Trap (Distractor Analysis):

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• Why not A?
  A local secondary index (LSI) shares the same partition key but can have a different sort key attribute. But here, the current sort key is already ItemsCount. Creating an LSI won’t change sort order; it helps if you want a different sort key or projection. Also, LSIs cannot change sort order direction.

• Why not B?
  Changing the sort key attribute name to ItemsCountDescending doesn’t inherently control result ordering. You must change data or client query parameters to control direction, so just renaming the attribute has no effect on ascending vs descending order.

• Why not D?
  The KeyConditionExpression defines which partition and sort key values to query but says nothing about sorting order. Setting it “to false” is not a valid parameter value and would cause an error.

The Technical Blueprint

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// Example AWS SDK v3 JavaScript snippet to query with descending order
import { DynamoDBClient, QueryCommand } from "@aws-sdk/client-dynamodb";

const client = new DynamoDBClient({});
const params = {
  TableName: "FinSightTransactions",
  KeyConditionExpression: "TransactionID = :tid",
  ExpressionAttributeValues: {
    ":tid": { N: "12345" }
  },
  ScanIndexForward: false  // <-- descending order on ItemsCount sort key
};

const command = new QueryCommand(params);
const data = await client.send(command);
console.log(data.Items);

The Comparative Analysis

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Real-World Application (Practitioner Insight)

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Exam Rule

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“For the exam, always pick option C when you see a sorting order question related to DynamoDB Query.”

Real World

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“In production, controlling result order at query time with ScanIndexForward saves costly schema changes or creating extra indexes, keeping your code agile and performant.”

(CTA) Stop Guessing, Start Mastering

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Disclaimer

This is a study note based on simulated scenarios for the AWS DVA-C02 exam.