Scan with filter expressions in DynamoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Scan with a simple filter expression

Given a DynamoDB table named Products with items having attributes Category and Price, what will be the output of this scan operation?

Scan with FilterExpression: Category = :cat
ExpressionAttributeValues: { ':cat': { S: 'Books' } }

DynamoDB

aws dynamodb scan --table-name Products --filter-expression "Category = :cat" --expression-attribute-values '{":cat":{"S":"Books"}}'

A Returns items where Category contains the substring 'Books'

B Returns all items regardless of Category

C Returns no items because filter expression is invalid

D Returns all items where Category is exactly 'Books'

💡 Hint

FilterExpression filters items after scanning all; it matches exact values unless using functions.

The filter expression 'Category = :cat' matches items where the Category attribute exactly equals 'Books'. It does not do substring matching or ignore the filter.

❓ query_result

intermediate

Scan with numeric filter expression

Consider a DynamoDB table Orders with attribute Amount (number). What will this scan return?

FilterExpression: Amount > :minAmount
ExpressionAttributeValues: { ':minAmount': { N: '100' } }

DynamoDB

aws dynamodb scan --table-name Orders --filter-expression "Amount > :minAmount" --expression-attribute-values '{":minAmount":{"N":"100"}}'

A All items with Amount greater than or equal to 100

B All items with Amount greater than 100

C All items with Amount less than 100

D No items because numeric comparison is not supported in filter expressions

💡 Hint

Filter expressions support numeric comparisons like >, <, =.

The filter expression 'Amount > :minAmount' returns items where Amount is strictly greater than 100.

📝 Syntax

advanced

Identify the syntax error in filter expression

Which option contains a syntax error in the DynamoDB scan filter expression?

DynamoDB

Scan command with filter expressions

A FilterExpression: "Price => :minPrice" with ExpressionAttributeValues { ':minPrice': {N: '15'} }

B FilterExpression: "contains(ProductName, :name)" with ExpressionAttributeValues { ':name': {S: 'Book'} }

C FilterExpression: "Category = :cat OR Price > :price" with ExpressionAttributeValues { ':cat': {S: 'Books'}, ':price': {N: '20'} }

D FilterExpression: "Price BETWEEN :low AND :high" with ExpressionAttributeValues { ':low': {N: '10'}, ':high': {N: '50'} }

💡 Hint

Check the comparison operator syntax carefully.

The operator '=>' is invalid in DynamoDB filter expressions. The correct operator for greater or equal is '>='.

❓ query_result

advanced

Scan with multiple filter conditions

What items will be returned by this scan?

FilterExpression: "Category = :cat AND Price BETWEEN :low AND :high"
ExpressionAttributeValues: { ':cat': { S: 'Electronics' }, ':low': { N: '100' }, ':high': { N: '500' } }

DynamoDB

aws dynamodb scan --table-name Products --filter-expression "Category = :cat AND Price BETWEEN :low AND :high" --expression-attribute-values '{":cat":{"S":"Electronics"},":low":{"N":"100"},":high":{"N":"500"}}'

A Items with Price between 100 and 500 only

B Items with Category 'Electronics' or Price between 100 and 500

C Items with Category 'Electronics' and Price between 100 and 500 inclusive

D No items because AND operator is not supported in filter expressions

💡 Hint

AND operator combines conditions that must all be true.

The filter expression requires both conditions to be true: Category equals 'Electronics' and Price is between 100 and 500 inclusive.

🧠 Conceptual

expert

Understanding scan with filter expressions and performance

Which statement best describes the behavior and performance impact of using filter expressions in DynamoDB scans?

A Filter expressions are applied after scanning all items, so they do not reduce read capacity units consumed.

B Filter expressions reduce the number of items read from the table, improving scan performance.

C Filter expressions prevent DynamoDB from scanning items that do not match the filter, saving costs.

D Filter expressions automatically create indexes to speed up scans.

💡 Hint

Think about when filtering happens during a scan operation.

Filter expressions are applied after DynamoDB reads all items, so they do not reduce the amount of data read or the read capacity units consumed. They only reduce the data returned to the client.