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BasicSQL~6 min

Find duplicate customer emails

Very common data-validation question for QA/ETL testers

Points available

100/100

Your mission

  1. Read
  2. 2Run
  3. 3Submit
  4. 4Solve

Return every email that belongs to more than one customer, with the number of customers as cnt.

Ignore NULL emails.

Runs on the QA Shop practice database (customers, products, orders, order_items, payments, employees, bugs, test_runs, audit_log). Each run starts from a fresh copy.

Hints

Each hint costs 10 points on a full solve.

Interviewer follow-ups

  • How would you delete the duplicates but keep the lowest id?

Ctrl+Enter to run · add Shift to submit

1
2
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Tab inserts two spaces. Press Escape, then Tab, to leave the editor.
Terminal

$ sqlite3 qa-shop.db < solution.sql

Run executes the open file. Submit scores solution.sql against hidden tests.

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