Topfolio
Career TracksJob Hunt TrackerMicro Free CoursesTask CoursesPracticeInterview PracticeWork ExperienceProjects
Career TrackBlog
Support
Dashboard
Career TracksMicro Free CoursesTask Courses
SQL & Python
Interview Prep
Job Hunt TrackerWork ExperienceProjectsResume Feedback
CertificatesMy OrdersRefer & Earn
Join Community

Navigation

Dashboard
Learn
Career TracksMicro Free CoursesTask Courses
Practice
SQL & PythonInterview Prep
Career
Job Hunt TrackerWork ExperienceProjectsResume Feedback
My Stuff
CertificatesMy OrdersRefer & Earn
Join Community
Topfolio

Learn data analytics online. Real skills, real projects, real community.

courses

  • Career Tracks
  • Work Experience
  • Best Data Analyst Course in India
  • SQL Fundamentals
  • SQL Advanced
  • Python for Data
  • Micro Free Courses

practice

  • SQL Fundamentals Interview Test
  • SQL Advanced Coding Test
  • All Practice Tests

resources

  • How to Become a Data Analyst
  • SQL Interview Questions
  • Data Analyst Salary Guide
  • Free Datasets for Practice
  • SQL vs NoSQL Guide
  • Data Analyst vs Data Engineer vs Data Scientist

employers

  • Enterprise Screening
  • AI Proctoring Demo
  • Volume Pricing
  • Employer Portal

company

  • About
  • Terms
© 2026 Topfolio. All rights reserved.Made with ❤️ for aspiring analysts
Topfolio
Career TracksJob Hunt TrackerMicro Free CoursesTask CoursesPracticeInterview PracticeWork ExperienceProjects
Career TrackBlog
Support
Dashboard
Career TracksMicro Free CoursesTask Courses
SQL & Python
Interview Prep
Job Hunt TrackerWork ExperienceProjectsResume Feedback
CertificatesMy OrdersRefer & Earn
Join Community

Navigation

Dashboard
Learn
Career TracksMicro Free CoursesTask Courses
Practice
SQL & PythonInterview Prep
Career
Job Hunt TrackerWork ExperienceProjectsResume Feedback
My Stuff
CertificatesMy OrdersRefer & Earn
Join Community

Self-Join: Customers in Same City

intermediate~9 min25 pts
📊 View Insights

Problem

Find pairs of customers who live in the same city. This can help with organizing local meetups or referral programs.

Write a self-join query to find customer pairs in the same city.

Schema: Customer

ColumnType
CustomerIdINTEGER (Primary Key)
FirstNameTEXT
LastNameTEXT
CompanyTEXT
AddressTEXT
CityTEXT
StateTEXT
CountryTEXT
PostalCodeTEXT
PhoneTEXT
FaxTEXT
EmailTEXT
SupportRepIdINTEGER (Foreign Key → Employee.EmployeeId)

Requirements:

  • Self-join Customer table on City
  • Avoid duplicate pairs (customer with themselves, or A-B and B-A)
  • Return Customer1Name, Customer2Name, and City
  • Limit to 15 rows

Avoiding Duplicates:

Use c1.CustomerId < c2.CustomerId to ensure each pair appears only once.

Self-JoinJOINDeduplication
📊
📊 View Question Telemetry & Insights
Failure rate, silent bug autopsy & optimal query construction
Inspect →

Master SQL & Data Analytics

Ready to take your skills to the next level? Enroll in our comprehensive Data Analyst Career Track to master SQL, Python, Excel, and Power BI.

Explore the 12-Week Data Analyst Career Track

Related questions

  • Albums with Artist Namesintermediate
  • Tracks with Genre Namesintermediate
  • Customer Purchase Historyintermediate
  • Track Count by Genreintermediate
  • Average Song Duration by Genreintermediate
  • Most Prolific Artistsintermediate
  • Rank Artists by Album Countintermediate
  • Segment Customers into Quartilesintermediate
SQL Editor

Run your code to see the result here.

Topfolio

Learn data analytics online. Real skills, real projects, real community.

courses

  • Career Tracks
  • Work Experience
  • Best Data Analyst Course in India
  • SQL Fundamentals
  • SQL Advanced
  • Python for Data
  • Micro Free Courses

practice

  • SQL Fundamentals Interview Test
  • SQL Advanced Coding Test
  • All Practice Tests

resources

  • How to Become a Data Analyst
  • SQL Interview Questions
  • Data Analyst Salary Guide
  • Free Datasets for Practice
  • SQL vs NoSQL Guide
  • Data Analyst vs Data Engineer vs Data Scientist

employers

  • Enterprise Screening
  • AI Proctoring Demo
  • Volume Pricing
  • Employer Portal

company

  • About
  • Terms
© 2026 Topfolio. All rights reserved.Made with ❤️ for aspiring analysts