select * from category

-- Sua table: Lap Trinh JS => Lap Trinh HTML/CSS/JS
update category set name = 'Lap Trinh HTML/CSS/JS'
where name = 'Lap Trinh JS'

update category set name = 'TEST' where name like '%Trinh%'

update category set name = 'Lap Trinh C' where id = 1
update category set name = 'Lap Trinh HTML/CSS/JS' where id = 3

delete from category

select * from student2

update student2 set rollno = 'R000' where rollno = ''
delete from student2 where rollno = 'R003'

alter table student2
add email nvarchar(150)

update student2 set email = 'gokisoft.com@gmail.com'

update student2 set email = null

alter table student2
add constraint unique_email unique (email)

select top(2) * from student2

select distinct firstname, lastname, address from student2

select firstname, lastname, address, count(firstname) as count_total
from student2
group by firstname, lastname, address
having count(firstname) > 1
order by count_total asc

alter table student2
add age int default 18

select firstname, lastname, address, avg(age) as avg_age
from student2
group by firstname, lastname, address

select firstname, lastname, address, sum(age) as sum_age
from student2
group by firstname, lastname, address

select firstname, lastname, address, min(age) as min_age
from student2
group by firstname, lastname, address

select firstname, lastname, address, max(age) as max_age
from student2
group by firstname, lastname, address

select firstname, lastname,address, age as 'Tuoi' from student2
where age <=19
order by 'Tuoi' asc
union
select firstname, lastname,address, age 'Tuoi' from student2
where age > 19