GROUP BY और HAVING

GROUP BY — हर Group का Summary

GROUP BY rows को groups में बाँटकर हर group पर aggregate लगाता है।

SELECT class, COUNT(*) AS total
FROM students
GROUP BY class;

हर Group का Average

SELECT class, AVG(marks) AS avg_marks
FROM students
GROUP BY class;

HAVING — Groups Filter करें

HAVING aggregation के बाद groups filter करता है (WHERE पहले rows filter करता है)।

SELECT class, AVG(marks) AS avg_marks
FROM students
GROUP BY class
HAVING AVG(marks) >= 80;

WHERE बनाम HAVING

सारांश

• GROUP BY groups बनाता है; aggregates हर group पर चलते हैं।
• HAVING groups filter करता है; WHERE grouping से पहले rows।