1、如果第二个表已经有这个记录了,就不插入,如果没有,就插入这条记录
create or replace trigger fortest
declare co number := 0;
begin
select count(1) into co from test2 where a = :new.a and b = :new.b;
if co = 0 then
insert into test2(a,b) values(:new.a,:new.b);
end if;
end;
2、找出名字相同的员工
select a,b from(
select count(1) a,e.empname b from emp e group by e.empname
) c where a>1 ;