easy5 pts · first answer countssqlconcurrency

Duplicate emails despite a check

Signup code runs SELECT to check whether the email exists and then INSERTs the user. Duplicate accounts still appear under heavy traffic. What is the right fix?

A.Add a short sleep between the check and the insertB.Add a UNIQUE constraint (or unique index) on email and handle the duplicate-key errorC.Run the SELECT check twice before insertingD.Wrap the SELECT and INSERT in one READ COMMITTED transaction so the check and the insert happen together

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