Dataford
Interview QuestionsInterview GuidesExperiencesCoaching
New
Pricing
Get started
Dataford
Popular roles
Software EngineerData AnalystData ScientistData EngineerBusiness AnalystAI EngineerMachine Learning EngineerProduct Manager
Browse
Browse All RolesEvery role hub, from analyst to MLBrowse All CompaniesCompany-specific interview loopsAll Interview GuidesThe full guide library
Top questions by role
Software EngineerData AnalystData ScientistData EngineerBusiness AnalystAI EngineerMachine Learning EngineerProduct Manager
Top questions by skill
SQLPythonStatisticsMachine LearningA/B TestingSystem DesignGenerative AIProduct SenseMetricsBehavioral
Browse all questions →Try a mock interview
Experiences
Practice
Mock InterviewsTimed interview simulations with feedbackCoaching1:1 coaching with people at your target companiesSuccess PathYour 6-week structured planModulesCurated lessons by topicWebinarsTalks from ex-Big Tech data leadsPlaygroundA free-form scratch editor
Learn
BlogInterview strategy and career adviceTech Job Market ReportHiring trends across data and AI rolesFor UniversitiesDataford for career centersAbout DatafordWho we are and how we build
Pricing
Build my plan
Optimize Large SQL Query
00:00
5 left

Optimize Large SQL Query

HardSQL · PostgreSQL

Problem

Describe your process for optimizing a slow-running SQL query that processes billions of rows at AWS.

Using the provided PostgreSQL tables, produce the optimized query and explain the validation process, including execution plans, filtering, joins, aggregation, and indexing considerations.

Output

  1. One row per active account, service, and request date in the requested date range.
  2. Return account_name, service_name, request_date, successful_requests, p95_latency_ms, successful_bytes, and daily_change.
  3. Sort by account_name, service_name, and request_date ascending.

Schema

aws_accounts
ColumnTypeDescription
account_idPKBIGINTAWS account identifier
account_nameVARCHAR(100)Display name for the account
owner_teamVARCHAR(100)Team responsible for the account
activeBOOLEANWhether the account is active
aws_services
ColumnTypeDescription
service_idPKBIGINTAWS service identifier
service_nameVARCHAR(100)AWS service name
api_requests
ColumnTypeDescription
request_idPKBIGINTUnique API request identifier
account_idBIGINTRequesting AWS account
service_idBIGINTAWS service handling the request
request_tsTIMESTAMPTZRequest timestamp
status_codeINTHTTP-style response status code
bytes_sentBIGINTResponse bytes sent
regionVARCHAR(50)AWS Region for the request
latency_msNUMERIC(12,3)Request latency in milliseconds
Tablesapi_requestsaws_accountsaws_services
Interviewer

Your question is Optimize Large SQL Query. Start with the requirements and the three tables in the Question tab.

Run and submit as often as you like. When you're ready, talk me through your approach or go straight to the code.

You need to log in / sign up to run or submit.
CodePostgreSQL
Sign up free to run your codeLog inLn 1
Run your query to see results here.