diff --git a/script.sql b/script.sql
new file mode 100644
index 0000000..f899183
Binary files /dev/null and b/script.sql differ
diff --git a/solution.sql b/solution.sql
new file mode 100644
index 0000000..635d21a
--- /dev/null
+++ b/solution.sql
@@ -0,0 +1,118 @@
+-- những cặp student-professor có dạy học nhau và số lớp mà họ có liên quan
+
+select pr.prof_id,
+		pr.prof_fname+' '+ pr.prof_lname 'prof name',
+		st.stud_id, 
+		count(*) as
+from student as st
+join enroll as en 
+	on st.stud_id = en.stud_id
+join class as cl 
+	on cl.class_id = en.class_id
+join progessor as pr
+	on pr.prof_id = cl.prof_id
+group by pr.prof_id,st.stud_id,pr.prof_fname+' '+ pr.prof_lname
+
+-- những course (distinct) mà 1 professor cụ thể đang dạy
+select distinct pr.prof_id, co.course_id, co.course_name 
+from progessor as pr
+join class as cl 
+	on pr.prof_id = cl.prof_id
+join course as co
+	on cl.course_id = co.course_id
+where pr.prof_id = 1
+
+-- cau 3 những course (distinct) mà 1 student cụ thể đang học
+select distinct st.stud_id,co.course_id, course_name
+from student as st
+join enroll as en
+	on st.stud_id = en.stud_id
+join class as cl
+	on cl.class_id = en.class_id
+join course as co 
+	on cl.course_id = co.course_id
+where st.stud_id = 1
+
+-- điểm số là A, B, C, D, E, F tương đương với 10, 8, 6, 4, 2, 0
+select *,
+CASE
+    WHEN grade = 'A' THEN 10
+    WHEN grade = 'B' THEN 8
+    WHEN grade = 'C' THEN 6
+	WHEN grade = 'D' THEN 4
+	WHEN grade = 'E' THEN 2
+    ELSE 0
+END
+as score
+from enroll
+
+-- điểm số trung bình của 1 học sinh cụ thể (quy ra lại theo chữ cái, và xếp loại học lực (weak nếu avg < 5, average nếu >=5 < 8, good nếu >=8 )
+select st.stud_id, 
+	CASE
+            WHEN grade.score < 5 THEN 'Weak'
+            WHEN grade.score >= 5 AND grade.score < 8 THEN 'Average'
+            WHEN grade.score >= 8 THEN 'Good'
+	END
+from student as st
+join (
+	select stud_id,avg(
+	CASE
+		WHEN grade = 'A' THEN 10
+		WHEN grade = 'B' THEN 8
+		WHEN grade = 'C' THEN 6
+		WHEN grade = 'D' THEN 4
+		WHEN grade = 'E' THEN 2
+		ELSE 0
+	END
+	) as 'score'
+	from enroll
+	group by stud_id
+) as grade 
+on st.stud_id = grade.stud_id
+
+-- điểm số trung bình của các class (quy ra lại theo chữ cái)
+select cl.class_id, 
+	case 
+		WHEN grade.score < 5 THEN 'Weak'
+        WHEN grade.score >= 5 AND grade.score < 8 THEN 'Average'
+        WHEN grade.score >= 8 THEN 'Good'
+	end
+from class as cl
+join (
+select class_id, avg(
+	case
+		WHEN grade = 'A' THEN 10
+		WHEN grade = 'B' THEN 8
+		WHEN grade = 'C' THEN 6
+		WHEN grade = 'D' THEN 4
+		WHEN grade = 'E' THEN 2
+		ELSE 0
+	end
+) as score
+from enroll
+group by class_id) as grade
+on cl.class_id = grade.class_id
+
+
+-- điểm số trung bình của các course (quy ra lại theo chữ cái)
+select cl.class_id, 
+	case 
+		WHEN grade.score < 5 THEN 'Weak'
+        WHEN grade.score >= 5 AND grade.score < 8 THEN 'Average'
+        WHEN grade.score >= 8 THEN 'Good'
+	end
+from class as cl
+join (
+select class_id, avg(
+	case
+		WHEN grade = 'A' THEN 10
+		WHEN grade = 'B' THEN 8
+		WHEN grade = 'C' THEN 6
+		WHEN grade = 'D' THEN 4
+		WHEN grade = 'E' THEN 2
+		ELSE 0
+	end
+) as score
+from enroll
+group by class_id) as grade
+on cl.class_id = grade.class_id