[DMDB] SQL basics completed

semester4/dmdb/code/sql/aggregations.sql

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+SELECT MAX(price) as MAX_PRICE FROM Products; -- Get the most expensive product
+SELECT AVG(grade) as AVG_GRADE FROM Exams WHERE id = 0; -- Get the average grade for an exam
+
+-- Aggregation with grouping (Remember, only aggregates and cols in GROUP BY clause can
+-- appear in SELECT clause!)
+SELECT id, AVG(grade) as "Average Grade", COUNT(grade) as "Count"
+FROM ExamResults GROUP BY id; -- Average grade for each exam and number of students taking it
+
+SELECT id, AVG(grade) as avg, COUNT(grade) as cnt FROM ExamResults
+GROUP BY id HAVING cnt > 0 ORDER BY avg DESC LIMIT 20;
+
+-- Get exam details for all exams as filtered before
+SELECT * FROM (
+    SELECT id, AVG(grade) as avg, COUNT(grade) as cnt FROM ExamResults
+    GROUP BY id HAVING cnt > 0 ORDER BY avg DESC LIMIT 20
+) as filtered JOIN Exams e ON filtered.id = e.id;