Query result ordering (ascending, descending) in DynamoDB - Step-by-Step Execution

Concept Flow - Query result ordering (ascending, descending)

Start Query

↓

Specify Partition Key

↓

Set ScanIndexForward

↓

Ascending

↓

Fetch Items in Order

↓

Return Results

The query starts by specifying the partition key, then sets the ScanIndexForward flag to true for ascending or false for descending order, fetches items accordingly, and returns the results.

Execution Sample

DynamoDB

Query(
  TableName='Orders',
  KeyConditionExpression='CustomerId = :cid',
  ExpressionAttributeValues={':cid': {'S': 'C123'}},
  ScanIndexForward=False
)

This query fetches orders for customer 'C123' in descending order by sort key.

Execution Table

Step	Action	ScanIndexForward	Order of Items Fetched	Result
1	Start Query with CustomerId = 'C123'	N/A	N/A	Query initialized
2	Set ScanIndexForward = False	False	Descending	Will fetch items from highest to lowest sort key
3	Fetch items matching CustomerId	False	Descending	Items fetched in descending order
4	Return results	False	Descending	Results returned in descending order
5	End	False	Descending	Query complete

💡 All matching items fetched and returned in descending order because ScanIndexForward is False

Variable Tracker

Variable	Start	After Step 2	After Step 3	Final
ScanIndexForward	N/A	False	False	False
Order of Items	N/A	N/A	Descending	Descending

Key Moments - 2 Insights

Why does setting ScanIndexForward to False return items in descending order?

Because ScanIndexForward controls the order of the sort key in the query result. False means descending order, as shown in execution_table step 2 and 3.

What happens if ScanIndexForward is not set?

By default, ScanIndexForward is True, so items are returned in ascending order of the sort key, as implied by the concept flow.

Visual Quiz - 3 Questions

Look at the execution_table at step 2, what is the value of ScanIndexForward?

A True

B False

C Null

D Not set

💡 Hint

Check the 'ScanIndexForward' column in execution_table row for step 2

At which step are items fetched in descending order?

A Step 1

B Step 2

C Step 3

D Step 5

💡 Hint

Look at the 'Order of Items Fetched' column in execution_table

If ScanIndexForward was set to True, how would the order of items change?

A Items would be fetched in ascending order

B Items would be fetched in descending order

C No items would be fetched

D Order would be random

💡 Hint

Refer to the key_moments explanation about default ScanIndexForward behavior

Concept Snapshot

DynamoDB Query ordering:
- Use ScanIndexForward parameter
- True = ascending order (default)
- False = descending order
- Applies to sort key ordering
- Must specify partition key in query

Full Transcript

This visual execution shows how DynamoDB query result ordering works. The query starts by specifying the partition key. Then the ScanIndexForward flag is set. If it is False, items are fetched in descending order by the sort key. If True or not set, items are fetched ascending. The execution table traces each step from query start to returning results. The variable tracker shows ScanIndexForward stays False and order is descending. Key moments clarify why ScanIndexForward controls order and what happens if not set. The quiz tests understanding of ScanIndexForward value and its effect on item order.