QuerydrillFind duplicate accounts
An SQL exercise from Querydrill. Solve it with a SQL editor in your browser, checked on the rows it returns and again on changed data, and it is checked the moment you submit.
The task
From Sam in Support: "Some people signed up more than once with the same email, typed differently (capitals, extra spaces). List each email that has more than one account, in lowercase with no spaces, and how many accounts it has. Most accounts first, then alphabetically." Return email and accounts.
What this exercise teaches
HAVING filters groups after they are counted. Normalizing before grouping is what makes typed-differently duplicates visible.
A hint if you get stuck
Clean the email with LOWER(TRIM(email)), group by it, and keep groups with HAVING COUNT(*) > 1.
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