SQL Question & Answer Practice

SQL Practice – Questions & Answers

Beginner Level

Q31. AND operator.

WHERE age>18 AND city='Delhi';

Q32. OR operator.

WHERE city='Delhi' OR city='Mumbai';

Q33. NOT operator.

WHERE NOT city='Delhi';

Q34. NULL check.

WHERE city IS NULL;

Q35. IS NOT NULL.

WHERE city IS NOT NULL;

Q36. LEFT JOIN.

SELECT * FROM a LEFT JOIN b ON a.id=b.id;

Q37. RIGHT JOIN.

SELECT * FROM a RIGHT JOIN b ON a.id=b.id;

Q38. UNION.

SELECT name FROM a UNION SELECT name FROM b;

Q39. UNION ALL.

UNION ALL

Q40. DROP table.

DROP TABLE students;

Q41. EXISTS.

WHERE EXISTS(SELECT 1 FROM marks);

Q42. Find duplicates.

SELECT name,COUNT(*) FROM students
GROUP BY name HAVING COUNT(*)>1;

Q43. Delete duplicates.

DELETE FROM students
WHERE id NOT IN (SELECT MIN(id) FROM students GROUP BY name);

Q44. TRANSACTION.

BEGIN; COMMIT;

Q45. ROLLBACK.

ROLLBACK;