Optimization of MySchool Database design Joint, join, sub-query

Use MySchool
Go

--Union query: Merging rows from multiple datasets
SELECT Studentno,subjectno,studentresult from Result
--union
SELECT Subjectno,classhour,gradeid from Subject

--Join query: Merge columns from multiple datasets
SELECT Studentname as name, Subjectno as course number, Studentresult as score
From Student INNER JOIN Result on student.studentno = Result.studentno

--Subquery: To filter records that match the criteria
SELECT * from Student WHERE Gradeid =
(SELECT Gradeid from Grade WHERE gradename = ' S1 ')

Optimization of MySchool Database design Joint, join, sub-query