SQL Having Examples

1-) List the class names and number of students which the number of students more than 30.

Solution 1)

Select sinif,count(*) as StudentCount 
from students 
group by sinif
having count(*) >= 30

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2-) List the name and surname of the students and the number of books they read sorted by BookCount. Also list the students who have never read a book.

Solution 1)

Select name,surname,count(borrowsno) BookCount 
from students
left join borrows on students.studentId = borrows.studentId 
group by students.studentId,name,surname
order by BookCount

Solution 2)

Select name, surname, 
	(Select count(*) from borrows 
		where students.studentId = borrows.studentId) as BookCount
from students 
order by BookCount

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Select - Top - Where - Having - Sub Query -

3-) Delete students who have read less than 5 books.

Solution 1)

Delete from students 
where studentId in (Select studentId from borrows 
                group by studentId 
				having count(*)<5)

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Delete - Where - Group By - Having - Sub Query -