Difference between Where and Having
Where vs Having
Where and Having are used as search conditions in a select statement or in a query.
Where clause is the search condition for the rows returned by the select statement.
Having clause is the search condition for a group or an aggregate.
Having clause is usually used with a GROUP BY clause.
select Title, Student_id
select Student_id, count(*) Nr
group by Student_id
having count(Student_id)>1 ;