Query result ordering (ascending, descending) in DynamoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the 'ScanIndexForward' parameter control in a DynamoDB query?

It controls the order of the query results. Setting it to true returns results in ascending order by sort key, and false returns results in descending order.

beginner

How do you get query results in descending order in DynamoDB?

Set the 'ScanIndexForward' parameter to false in your query request.

beginner

True or False: DynamoDB query results are always returned in ascending order by default.

True. By default, 'ScanIndexForward' is true, so results come back in ascending order by sort key.

intermediate

If you want to see the newest items first in a DynamoDB query, what should you do?

Set 'ScanIndexForward' to false to get results in descending order, showing newest items first if your sort key is time-based.

beginner

What happens if you omit the 'ScanIndexForward' parameter in a DynamoDB query?

The query returns results in ascending order by default because 'ScanIndexForward' defaults to true.

In DynamoDB, which parameter controls the order of query results?

A ScanIndexForward

B OrderBy

C SortOrder

D ResultOrder

The 'ScanIndexForward' parameter controls whether query results are ascending (true) or descending (false).

What is the default order of query results in DynamoDB if 'ScanIndexForward' is not set?

A Descending

B Ascending

C Random

D No order

By default, 'ScanIndexForward' is true, so results come back in ascending order.

To get the latest records first in a DynamoDB query, you should set 'ScanIndexForward' to:

A false

B true

C null

D 1

Setting 'ScanIndexForward' to false returns results in descending order, showing newest items first if sorted by time.

If your sort key is a timestamp, which 'ScanIndexForward' value shows oldest items first?

A false

B undefined

C true

D null

True means ascending order, so oldest timestamps appear first.

Which of these is NOT a valid value for 'ScanIndexForward' in DynamoDB?

A null

B false

C true

D "ascending"

'ScanIndexForward' only accepts boolean true or false, not strings like "ascending".

Explain how to control the order of query results in DynamoDB and what the default behavior is.

Think about the boolean parameter that controls sorting direction.

Describe a real-life example where you would want to set 'ScanIndexForward' to false in a DynamoDB query.

Consider when you want to see the latest data at the top.

Practice

1. In DynamoDB, which parameter controls whether query results are returned in ascending or descending order based on the sort key?

easy

A. ProjectionExpression

B. ReturnConsumedCapacity

C. ScanIndexForward

D. ConsistentRead

Solution

1. Step 1: Understand query ordering in DynamoDB

   DynamoDB orders query results based on the sort key, and the order can be controlled.

2. Step 2: Identify the controlling parameter

   The parameter ScanIndexForward controls ascending (true) or descending (false) order.

3. Final Answer:

   ScanIndexForward -> Option C

4. Quick Check:

   Ordering parameter = ScanIndexForward [OK]

Hint: Remember: ScanIndexForward controls ascending/descending order [OK]

Common Mistakes:

• Confusing ScanIndexForward with ReturnConsumedCapacity
• Thinking ordering applies to partition key
• Assuming default order is descending

2. Which of the following is the correct syntax to query a DynamoDB table named Orders with results in descending order on the sort key OrderDate?

easy

A. client.query({ TableName: 'Orders', KeyConditionExpression: 'CustomerId = :id', ExpressionAttributeValues: { ':id': '123' }, ScanIndexForward: true })

B. client.query({ TableName: 'Orders', KeyConditionExpression: 'CustomerId = :id', ExpressionAttributeValues: { ':id': '123' }, ScanIndexForward: false })

C. client.query({ TableName: 'Orders', KeyConditionExpression: 'CustomerId = :id', ExpressionAttributeValues: { ':id': '123' }, Descending: true })

D. client.query({ TableName: 'Orders', KeyConditionExpression: 'CustomerId = :id', ExpressionAttributeValues: { ':id': '123' }, OrderBy: 'DESC' })

Solution

1. Step 1: Identify the parameter for descending order

   To get descending order, ScanIndexForward must be set to false.

2. Step 2: Check the syntax correctness

   client.query({ TableName: 'Orders', KeyConditionExpression: 'CustomerId = :id', ExpressionAttributeValues: { ':id': '123' }, ScanIndexForward: false }) uses ScanIndexForward: false correctly; other options use invalid or wrong parameters.

3. Final Answer:

   Option B syntax with ScanIndexForward false -> Option B

4. Quick Check:

   Descending order = ScanIndexForward false [OK]

Hint: Use ScanIndexForward false for descending order [OK]

Common Mistakes:

• Using ScanIndexForward true for descending order
• Using non-existent parameters like Descending or OrderBy
• Confusing partition key with sort key ordering

3. Given a DynamoDB table with partition key UserId and sort key Timestamp, what will be the order of results returned by this query?

client.query({
  TableName: 'UserActivity',
  KeyConditionExpression: 'UserId = :uid',
  ExpressionAttributeValues: { ':uid': 'user123' },
  ScanIndexForward: false
})

medium

A. Results unordered

B. Results ordered by Timestamp ascending (oldest first)

C. Results ordered by UserId ascending

D. Results ordered by Timestamp descending (newest first)

Solution

1. Step 1: Understand ScanIndexForward effect

   Setting ScanIndexForward: false returns results in descending order of the sort key.

2. Step 2: Identify the sort key

   The sort key is Timestamp, so results are ordered newest to oldest.

3. Final Answer:

   Results ordered by Timestamp descending (newest first) -> Option D

4. Quick Check:

   ScanIndexForward false = descending order [OK]

Hint: ScanIndexForward false means newest items first [OK]

Common Mistakes:

• Assuming ScanIndexForward false orders by partition key
• Thinking default order is descending
• Confusing ascending and descending meanings

4. You wrote this DynamoDB query but the results are always in ascending order, even though you want descending order:

client.query({
  TableName: 'Sales',
  KeyConditionExpression: 'StoreId = :sid',
  ExpressionAttributeValues: { ':sid': 'store1' },
  ScanIndexForward: 'false'
})

What is the error?

medium

A. ScanIndexForward must be a boolean, not a string

B. KeyConditionExpression is incorrect

C. ExpressionAttributeValues is missing a value

D. TableName is invalid

Solution

1. Step 1: Check ScanIndexForward data type

   ScanIndexForward expects a boolean true or false, not a string.

2. Step 2: Identify impact of wrong type

   Passing 'false' as a string is truthy, so DynamoDB treats it as true (ascending order).

3. Final Answer:

   ScanIndexForward must be boolean false, not string 'false' -> Option A

4. Quick Check:

   Boolean type needed for ScanIndexForward [OK]

Hint: Use boolean false, not string 'false' for ScanIndexForward [OK]

Common Mistakes:

• Passing 'false' as a string instead of boolean
• Misunderstanding KeyConditionExpression syntax
• Ignoring data types in parameters

5. You want to retrieve the 5 most recent orders for customer cust123 from a DynamoDB table Orders with partition key CustomerId and sort key OrderDate. Which query will correctly return these orders in descending order by OrderDate?

hard

A. client.query({ TableName: 'Orders', KeyConditionExpression: 'CustomerId = :cid', ExpressionAttributeValues: { ':cid': 'cust123' }, ScanIndexForward: false, Limit: 5 })

B. client.query({ TableName: 'Orders', KeyConditionExpression: 'CustomerId = :cid', ExpressionAttributeValues: { ':cid': 'cust123' }, ScanIndexForward: false })

C. client.query({ TableName: 'Orders', KeyConditionExpression: 'CustomerId = :cid', ExpressionAttributeValues: { ':cid': 'cust123' }, Limit: 5 })

D. client.query({ TableName: 'Orders', KeyConditionExpression: 'CustomerId = :cid', ExpressionAttributeValues: { ':cid': 'cust123' }, ScanIndexForward: true, Limit: 5 })

Solution

1. Step 1: Set descending order for most recent first

   Use ScanIndexForward: false to get descending order by OrderDate.

2. Step 2: Limit results to 5

   Use Limit: 5 to get only the top 5 recent orders.

3. Final Answer:

   Query with ScanIndexForward false and Limit 5 -> Option A

4. Quick Check:

   Descending + Limit 5 = ScanIndexForward false + Limit 5 [OK]

Hint: Use ScanIndexForward false with Limit 5 for recent 5 items [OK]

Common Mistakes:

• Using ScanIndexForward true returns oldest first
• Omitting Limit returns all items
• Not combining descending order with limit