In SQL, IN and EXISTS are used for subquery comparisons, but they work differently. IN compares a value against a static list, while EXISTS checks for the presence of rows from a subquery. Understanding the difference is essential for writing optimised and correct SQL queries.
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Which one uses a correlated subquery more efficiently?
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Question 4 of 15
4. Question
What does EXISTS return if the subquery has 0 rows?
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Question 5 of 15
5. Question
What happens if the IN subquery contains NULLs?
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Question 6 of 15
6. Question
Which one generally performs better on large datasets?
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Question 7 of 15
7. Question
Choose the correct syntax for EXISTS:
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Question 8 of 15
8. Question
Which query checks if a customer placed any orders?
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Question 9 of 15
9. Question
When is IN more readable and better suited?
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Question 10 of 15
10. Question
What does this return?
SELECT name FROM emp WHERE dept_id IN (SELECT id FROM dept WHERE location = ‘NY’);
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Question 11 of 15
11. Question
Which one stops scanning as soon as a match is found?
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Question 12 of 15
12. Question
Which is true about IN and EXISTS?
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Question 13 of 15
13. Question
Which can be affected by NULL values in the subquery?
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Question 14 of 15
14. Question
What does this query do?
SELECT * FROM products WHERE EXISTS (SELECT * FROM reviews WHERE reviews.product_id = products.id);
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Question 15 of 15
15. Question
Which is preferred when dealing with subqueries involving multiple joins and large data?
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Summary
Understanding the difference between SQL’s IN and EXISTS helps avoid performance issues and logic bugs—especially when dealing with NULLs and correlated subqueries.
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