50 Important MySQL Queries

Practice Queries (Set 1)

Basic SELECT और WHERE

1.  SELECT * FROM students;
2.  SELECT name, marks FROM students;
3.  SELECT * FROM students WHERE marks >= 90;
4.  SELECT * FROM students WHERE class = '10';
5.  SELECT * FROM students WHERE marks BETWEEN 60 AND 80;
6.  SELECT * FROM students WHERE name LIKE 'A%';
7.  SELECT * FROM students WHERE city IN ('Delhi','Agra');
8.  SELECT DISTINCT class FROM students;
9.  SELECT * FROM students ORDER BY marks DESC;
10. SELECT * FROM students ORDER BY marks DESC LIMIT 3;

Aggregates और Grouping

11. SELECT COUNT(*) FROM students;
12. SELECT AVG(marks) FROM students;
13. SELECT MAX(marks), MIN(marks) FROM students;
14. SELECT class, COUNT(*) FROM students GROUP BY class;
15. SELECT class, AVG(marks) FROM students GROUP BY class HAVING AVG(marks)>75;

Data बदलना

16. INSERT INTO students VALUES (51,'New','10',88,'Agra');
17. UPDATE students SET marks=95 WHERE roll_no=1;
18. DELETE FROM students WHERE marks<33;
19. SELECT name, CASE WHEN marks>=33 THEN 'Pass' ELSE 'Fail' END AS res FROM students;
20. SELECT class, COUNT(*) FROM students GROUP BY class ORDER BY 2 DESC;

और Try करें

21–50: हर city के students गिनें, हर class का topper (window functions), बिना city वाले (IS NULL), दूसरा-सबसे-ऊँचा mark (LIMIT 1 OFFSET 1), और fees table के साथ joins। पूरी practice के लिए इन्हें खुद बनाएं।

सारांश

• SELECT, WHERE, ORDER, LIMIT, aggregates, GROUP BY/HAVING, INSERT/UPDATE/DELETE, CASE cover करता है।
• हर query पहले खुद लिखें, फिर output verify करें।