1427. Insert if missing — School ERP — implementation variant 27

DBMS Published 30 Sept 2026 Updated 30 Sept 2026 0 Views Verified

In a School ERP application, implement this production problem: Insert a customer only when an email does not already exist. The API/service receives user input and must return or modify data safely. Give the SQL solution, explain why it works, and show how the same operation is called from the selected stack.

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Answer & Explanation

4 Answers

Verified

Option A

UPDATE the_table SET status='active';

Additional Explanation

Incorrect: it does not implement the stated business rule and may modify/fetch the wrong rows.

Verified

Option B

SELECT * FROM the_table;

Additional Explanation

Incorrect: it does not implement the stated business rule and may modify/fetch the wrong rows.

Verified

Option C

DELETE FROM the_table;

Additional Explanation

Incorrect: it does not implement the stated business rule and may modify/fetch the wrong rows.

Verified Correct Answer

Option D

INSERT INTO customers(name,email,status) SELECT :name,:email,'active' WHERE NOT EXISTS (SELECT 1 FROM customers WHERE email=:email);

Additional Explanation

This statement helps, but a UNIQUE constraint on email is still required for race-safe enforcement.