The following is the script to create user and required schema objects.
create user er identified by er;
grant all privileges to er;
connect er/er
create table users
( username varchar(10) primary key,
password varchar2(10) not null,
email varchar2(50) unique
);
create table events
( eventid nuumber(5) primary key,
username varchar2(10) references users(username),
eventdesc varchar2(100),
eventdate date,
informbefore number(3),
eventtype char(1) check( eventtype in ('r','o'))
);
create sequence eventid_sequence start with 1 increment by 1 nocache;