Scan with filter expressions in DynamoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does a Scan operation do in DynamoDB?

A Scan reads every item in a table and returns all data attributes by default. It examines all items, which can be slow for large tables.

beginner

What is a Filter Expression in a DynamoDB Scan?

A Filter Expression lets you specify conditions to filter the results returned by a Scan. It does not reduce the read workload but filters data after reading.

beginner

How does a Filter Expression affect the data returned by a Scan?

It filters out items that don't match the condition after scanning all items. Only matching items are returned to you.

intermediate

Why might using a Filter Expression still be costly in DynamoDB?

Because Scan reads all items before filtering, it consumes read capacity for every item scanned, even if many are filtered out.

beginner

Give an example of a simple Filter Expression in a DynamoDB Scan.

Example: To find items where attribute 'status' equals 'active', use FilterExpression: "#s = :val" with ExpressionAttributeNames: {"#s": "status"} and ExpressionAttributeValues: {":val": "active"}.

What does a Filter Expression do in a DynamoDB Scan?

A Indexes items for faster search

B Filters items after scanning all items

C Deletes items that don't match

D Prevents scanning items that don't match

Filter Expressions filter the results after scanning all items; they do not prevent scanning.

Which statement is true about Scan with Filter Expression?

A Filter Expression reduces read capacity used

B Scan only reads items matching the filter

C Scan reads all items, then filters results

D Filter Expression changes table data

Scan reads all items in the table, then applies the Filter Expression to filter results.

Why might Scan with Filter Expression be inefficient?

A Because it reads all items before filtering

B Because it writes data multiple times

C Because it uses indexes incorrectly

D Because it deletes filtered items

Scan reads every item, which can be slow and costly, even if many are filtered out.

What is needed to use a Filter Expression in DynamoDB Scan?

A No extra parameters

B Only FilterExpression

C Only ExpressionAttributeNames

D FilterExpression and ExpressionAttributeValues

You need both FilterExpression and ExpressionAttributeValues to specify conditions and values.

If you want to find items where 'age' > 30 using Scan, what would you use?

A FilterExpression: "age > :val", ExpressionAttributeValues: {":val": 30}

B KeyConditionExpression: "age > 30"

C ProjectionExpression: "age > 30"

D UpdateExpression: "age > 30"

FilterExpression with ExpressionAttributeValues is used to filter items after scanning.

Explain how a Scan with Filter Expression works in DynamoDB and why it might be costly.

Think about when filtering happens during the Scan process.

Describe a simple example of using a Filter Expression in a DynamoDB Scan operation.

Focus on the syntax and purpose of FilterExpression.