Sort key purpose and usage in DynamoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to specify the sort key attribute name in a DynamoDB table creation.

DynamoDB

KeySchema=[{'AttributeName': 'UserId', 'KeyType': 'HASH'}, {'AttributeName': '[1]', 'KeyType': 'RANGE'}]

Drag options to blanks, or click blank then click option'

AUserId

BStatus

CTimestamp

DEmail

Attempts:

3 left

💡 Hint

Common Mistakes

Using the same attribute name for both partition and sort keys.

Choosing an attribute that does not help sort the data.

The sort key is often used to sort items with the same partition key. 'Timestamp' is a common choice for a sort key.

2fill in blank

medium

Complete the query to get all items with a specific partition key and sort key greater than a value.

DynamoDB

KeyConditionExpression = Key('UserId').eq('user123') & Key('Timestamp').[1]('2023-01-01T00:00:00Z')

Drag options to blanks, or click blank then click option'

Alt

Bgt

Ceq

Dbegins_with

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'lt' which means less than.

Using 'eq' which means equal to only.

The 'gt' operator means 'greater than', which filters items with sort key values after the given timestamp.

3fill in blank

hard

Fix the error in the query condition to correctly filter items by sort key prefix.

DynamoDB

KeyConditionExpression = Key('UserId').eq('user123') & Key('Timestamp').[1]('2023-01')

Drag options to blanks, or click blank then click option'

Agt

Beq

Clt

Dbegins_with

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'eq' which requires exact match.

Using 'gt' or 'lt' which compare full values, not prefixes.

The 'begins_with' function filters items where the sort key starts with the given prefix, useful for date prefixes.

4fill in blank

hard

Fill both blanks to create a DynamoDB table with a partition key 'OrderId' and a sort key 'OrderDate'.

DynamoDB

AttributeDefinitions=[{'AttributeName': '[1]', 'AttributeType': 'S'}, {'AttributeName': '[2]', 'AttributeType': 'S'}]

Drag options to blanks, or click blank then click option'

AOrderId

BOrderDate

CCustomerId

DStatus

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing attribute names that are not keys.

Not defining both keys in AttributeDefinitions.

Both 'OrderId' and 'OrderDate' must be defined as attributes with type 'S' (string) before using them as keys.

5fill in blank

hard

Fill all three blanks to query items with partition key 'ProductId', sort key greater than '2023-01-01', and project only 'Price' and 'Stock'.

DynamoDB

response = table.query(KeyConditionExpression=Key('[1]').eq('prod123') & Key('[2]').[3]('2023-01-01'), ProjectionExpression='Price, Stock')

Drag options to blanks, or click blank then click option'

AProductId

BTimestamp

Cgt

DCreatedAt

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong attribute names for keys.

Using 'eq' instead of 'gt' for filtering sort key.

'ProductId' is the partition key, 'CreatedAt' is the sort key attribute, and 'gt' filters items with sort key values greater than the date.

Practice

1. What is the main purpose of a sort key in a DynamoDB table?

easy

A. To store large binary data efficiently

B. To uniquely identify each item across all partitions

C. To organize and order items within the same partition key

D. To encrypt data at rest automatically

Solution

1. Step 1: Understand partition and sort keys roles

   The partition key groups items, and the sort key orders items within that group.

2. Step 2: Identify the sort key's purpose

   The sort key organizes related items so they can be retrieved in order and filtered efficiently.

3. Final Answer:

   To organize and order items within the same partition key -> Option C

4. Quick Check:

   Sort key = Organize items in partition [OK]

Hint: Sort key orders items inside a partition [OK]

Common Mistakes:

• Confusing sort key with partition key uniqueness
• Thinking sort key encrypts data
• Assuming sort key stores large binary data

2. Which of the following is the correct way to define a DynamoDB table with a partition key named UserID and a sort key named Timestamp using AWS CLI?

easy

A. aws dynamodb create-table --table-name MyTable --attribute-definitions AttributeName=Timestamp,AttributeType=N --key-schema AttributeName=Timestamp,KeyType=HASH --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5

B. aws dynamodb create-table --table-name MyTable --attribute-definitions AttributeName=UserID,AttributeType=S AttributeName=Timestamp,AttributeType=N --key-schema AttributeName=UserID,KeyType=HASH AttributeName=Timestamp,KeyType=HASH --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5

C. aws dynamodb create-table --table-name MyTable --attribute-definitions AttributeName=UserID,AttributeType=S --key-schema AttributeName=UserID,KeyType=RANGE --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5

D. aws dynamodb create-table --table-name MyTable --attribute-definitions AttributeName=UserID,AttributeType=S AttributeName=Timestamp,AttributeType=N --key-schema AttributeName=UserID,KeyType=HASH AttributeName=Timestamp,KeyType=RANGE --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5

Solution

1. Step 1: Check attribute definitions and key schema

   Partition key must have KeyType=HASH and sort key must have KeyType=RANGE.

2. Step 2: Verify aws dynamodb create-table --table-name MyTable --attribute-definitions AttributeName=UserID,AttributeType=S AttributeName=Timestamp,AttributeType=N --key-schema AttributeName=UserID,KeyType=HASH AttributeName=Timestamp,KeyType=RANGE --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5 matches correct key types

   aws dynamodb create-table --table-name MyTable --attribute-definitions AttributeName=UserID,AttributeType=S AttributeName=Timestamp,AttributeType=N --key-schema AttributeName=UserID,KeyType=HASH AttributeName=Timestamp,KeyType=RANGE --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5 uses UserID as HASH and Timestamp as RANGE, which is correct.

3. Final Answer:

   aws dynamodb create-table --table-name MyTable --attribute-definitions AttributeName=UserID,AttributeType=S AttributeName=Timestamp,AttributeType=N --key-schema AttributeName=UserID,KeyType=HASH AttributeName=Timestamp,KeyType=RANGE --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5 -> Option D

4. Quick Check:

   Partition=HASH, Sort=RANGE in CLI [OK]

Hint: Sort key uses KeyType=RANGE in key schema [OK]

Common Mistakes:

• Using KeyType=HASH for both keys
• Missing sort key in key schema
• Defining only partition key without sort key

3. Given a DynamoDB table with partition key UserID and sort key OrderDate, what will the following query return?

aws dynamodb query --table-name Orders --key-condition-expression "UserID = :uid AND OrderDate > :date" --expression-attribute-values '{":uid":{"S":"user123"}, ":date":{"S":"2023-01-01"}}'

medium

A. All orders for user123 with OrderDate after 2023-01-01, sorted by OrderDate

B. All orders for user123 regardless of OrderDate

C. All orders with OrderDate after 2023-01-01 for all users

D. Syntax error due to missing partition key in condition

Solution

1. Step 1: Analyze the key condition expression

   The query filters items where UserID equals 'user123' and OrderDate is greater than '2023-01-01'.

2. Step 2: Understand query behavior with partition and sort keys

   Query returns items for one partition key, ordered by sort key, filtered by the condition on sort key.

3. Final Answer:

   All orders for user123 with OrderDate after 2023-01-01, sorted by OrderDate -> Option A

4. Quick Check:

   Query filters by partition and sort key conditions [OK]

Hint: Query needs partition key equality and sort key condition [OK]

Common Mistakes:

• Expecting query to filter across all partitions
• Ignoring sort key condition in query
• Confusing query with scan operation

4. You wrote this DynamoDB query but it returns an error:

aws dynamodb query --table-name Sales --key-condition-expression "OrderID > :oid" --expression-attribute-values '{":oid":{"S":"1000"}}'

What is the likely cause?

medium

A. Using > operator on partition key is allowed

B. Missing partition key equality condition in key-condition-expression

C. Incorrect data type for expression attribute value

D. Missing sort key in attribute definitions

Solution

1. Step 1: Recall query key condition requirements

   DynamoDB query requires partition key equality condition in key-condition-expression.

2. Step 2: Identify error cause

   Query uses only 'OrderID > :oid' without partition key equality, causing error.

3. Final Answer:

   Missing partition key equality condition in key-condition-expression -> Option B

4. Quick Check:

   Partition key equality is mandatory in query [OK]

Hint: Query must have partition key equality condition [OK]

Common Mistakes:

• Using range operators on partition key
• Omitting partition key in query condition
• Confusing query with scan operation

5. You want to model a one-to-many relationship where each CustomerID can have multiple Invoices sorted by InvoiceDate. Which DynamoDB table design best uses the sort key to achieve this?

hard

A. Partition key: CustomerID, Sort key: InvoiceDate

B. Partition key: InvoiceDate, Sort key: CustomerID

C. Partition key: CustomerID only, no sort key

D. Partition key: InvoiceID, Sort key: InvoiceDate

Solution

1. Step 1: Understand one-to-many modeling in DynamoDB

   Use partition key for the 'one' side and sort key to order the 'many' items.

2. Step 2: Apply to CustomerID and Invoices

   CustomerID as partition key groups invoices; InvoiceDate as sort key orders them.

3. Final Answer:

   Partition key: CustomerID, Sort key: InvoiceDate -> Option A

4. Quick Check:

   Sort key models one-to-many order [OK]

Hint: Partition key = one side, sort key = many side order [OK]

Common Mistakes:

• Swapping partition and sort keys
• Not using sort key for ordering
• Using only partition key losing order info