Key condition expressions in DynamoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Query with simple partition key condition

Given a DynamoDB table named Orders with OrderID as the partition key, what will be the output of this key condition expression?

OrderID = :orderId

Assuming :orderId is set to 12345 and the table contains one item with OrderID 12345 and CustomerName 'Alice'.

DynamoDB

KeyConditionExpression: 'OrderID = :orderId',
ExpressionAttributeValues: { ':orderId': { N: '12345' } }

A Returns all items because partition key is ignored in key condition.

B Returns items with OrderID greater than 12345.

C Returns the item with OrderID 12345 and CustomerName 'Alice'.

D Returns no items because the key condition syntax is invalid.

💡 Hint

Remember, the key condition expression must specify the partition key equality.

In DynamoDB, the key condition expression must include the partition key with equality. Here, it matches the item with OrderID 12345 exactly.

❓ query_result

intermediate

Using sort key with BETWEEN in key condition

Consider a DynamoDB table Events with UserID as partition key and EventDate as sort key (string in 'YYYY-MM-DD' format). What will this key condition expression return?

UserID = :uid AND EventDate BETWEEN :start AND :end

With values:
:uid = 'user1'
:start = '2023-01-01'
:end = '2023-01-31'

The table has events for user1 on '2023-01-10', '2023-02-01', and '2023-01-20'.

DynamoDB

KeyConditionExpression: 'UserID = :uid AND EventDate BETWEEN :start AND :end',
ExpressionAttributeValues: { ':uid': { S: 'user1' }, ':start': { S: '2023-01-01' }, ':end': { S: '2023-01-31' } }

A Returns events on '2023-01-10' and '2023-01-20' for user1.

B Returns all events for user1 regardless of date.

C Returns only the event on '2023-02-01' for user1.

D Returns no events because BETWEEN is not valid in key condition.

💡 Hint

BETWEEN works on sort keys to filter a range of values.

The key condition filters items with UserID 'user1' and EventDate between '2023-01-01' and '2023-01-31', so it returns the two events within that date range.

📝 Syntax

advanced

Identify syntax error in key condition expression

Which option contains a syntax error in the DynamoDB key condition expression?

A UserID = :uid AND begins_with(EventDate, :prefix)

B UserID = :uid OR EventDate = :date

C UserID = :uid AND EventDate > :date

D UserID = :uid AND EventDate BETWEEN :start AND :end

💡 Hint

Key condition expressions only allow AND, not OR.

DynamoDB key condition expressions do not support OR operators. Option B uses OR, which is invalid syntax.

❓ query_result

advanced

Effect of missing partition key in key condition

What happens if you run a DynamoDB query with this key condition expression?

EventDate = :date

Given that EventDate is the sort key and UserID is the partition key.

DynamoDB

KeyConditionExpression: 'EventDate = :date',
ExpressionAttributeValues: { ':date': { S: '2023-01-01' } }

A Query returns all items with EventDate '2023-01-01' across all users.

B Query returns all items in the table.

C Query returns no items because sort key alone cannot be used.

D Query fails with an error because partition key is missing.

💡 Hint

Partition key equality is mandatory in key condition expressions.

DynamoDB requires the partition key equality condition in key condition expressions. Omitting it causes a validation error.

🧠 Conceptual

expert

Understanding key condition expression limitations

Which statement correctly describes a limitation of DynamoDB key condition expressions?

A Key condition expressions must include the partition key with equality and can optionally include sort key conditions.

B Key condition expressions can filter on any attribute, including non-key attributes.

C Key condition expressions support OR operators to combine multiple conditions.

D Key condition expressions can use any comparison operator on the partition key.

💡 Hint

Think about what is mandatory and optional in key condition expressions.

Key condition expressions require the partition key equality condition and optionally allow conditions on the sort key. They do not support OR or filtering on non-key attributes.