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
Top Three Customers Query
00:00
5 left

Top Three Customers Query

MediumSQL · PostgreSQL

Problem

Write a SQL query to find the top three customers based on purchase frequency.

Assume purchase frequency means the number of completed purchases. Exclude cancelled or otherwise non-completed purchases, and use the customer ID as the tie-breaker.

Output

  1. One row per customer with customer_id, customer_name, and purchase_frequency.
  2. Return the top three customers, ordered by purchase frequency descending and customer ID ascending for ties.

Schema

customers
ColumnTypeDescription
customer_idPKINTUnique customer identifier
customer_nameVARCHAR(100)Customer's display name
purchases
ColumnTypeDescription
purchase_idPKINTUnique purchase identifier
customer_idINTCustomer associated with the purchase
purchase_statusVARCHAR(20)Purchase processing status
Tablescustomerspurchases
Interviewer

Your question is Top Three Customers Query. Start with the requirements and the two 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.