SQL constraint 제약조건 (fk, pk, unique, default, check)

select * from insert_test
select * from insert_test2

//primary key
alter table insert_test2 add primary key (seq)
alter table insert_test2 drop primary key 

//foreign key
alter table insert_test2 
add constraint name_fk
foreign key (name) references insert_test (name)
alter table insert_test2 drop key name_fk

//unique
alter table insert_test2
add constraint table_pk
unique (cont, name)
alter table insert_test2 drop key table_pk

//check
alter table insert_test2
add constraint table_chk
check (seq >= 2)
alter table insert_test2 drop constraint table_chk

//default
alter table insert_test2 alter column name set default 'N'
alter table insert_test2 alter column name drop default