[Solved] You wrote this query to get all comments for a post in a single-table design DynamoDB table:KeyConditionExpression: PK = 'POST#123' AND SK = 'COMMENT#'Why does this query return no results? | DynamoDB

DynamoDB - Access Patterns and Query Optimization

You wrote this query to get all comments for a post in a single-table design DynamoDB table:

KeyConditionExpression: PK = 'POST#123' AND SK = 'COMMENT#'

Why does this query return no results?

ABecause SK uses '=' instead of 'begins_with' to match multiple comments.

BBecause PK should be 'COMMENT#' and SK should be 'POST#123'.

CBecause the table does not support queries on SK.

DBecause the query syntax is missing a FilterExpression.

Step-by-Step Solution

Solution:

Step 1: Analyze the KeyConditionExpression
The query uses SK = 'COMMENT#', which looks for an exact match on SK.
Step 2: Understand why no results appear
Comments likely have SK starting with 'COMMENT#' plus an ID, so exact match fails. Using 'begins_with' on SK is needed to get all comments.
Final Answer:
Because SK uses '=' instead of 'begins_with' to match multiple comments. -> Option A
Quick Check:
Use begins_with for multiple SK matches [OK]

Quick Trick: Use begins_with for partial sort key matches [OK]

Common Mistakes:

MISTAKES

Master "Access Patterns and Query Optimization" in DynamoDB

9 interactive learning modes - each teaches the same concept differently

More DynamoDB Quizzes

You wrote this query to get all comments for a post in a single-table design DynamoDB table: