Вы можете сделать это без использования regexp_like.
Lower
select * from test where lower(substr(email_address,instr(email_address,'@')+1))=lower('HotMail.com');
Это вернет результаты быстрее по сравнению с regexp_like, поскольку вы делаете точное совпадение.
РЕДАКТИРОВАТЬ
create or replace procedure PR_Q3
(old_email in varchar2, new_email in varchar2)
authid current_user
is
cursor E_info is select Email_Address from test where lower(substr(email_address,instr(email_address,'@')+1))=lower(old_email);
v_email E_info%rowtype;
begin
open E_info;
loop
fetch E_info into v_email;
exit when E_info%notfound;
update test set
Email_Address = replace(Email_Address,substr(Email_Address,instr(Email_Address,'@')+1),new_email)
where Email_Address = v_email.Email_Address;
end loop;
close E_info;
end PR_Q3;
/