Add foreign key in table definition
create table offerings ( course VARCHAR2(6) constraint O_COURSE_NN not null constraint O_COURSE_FK references courses , begindate DATE constraint O_BEGIN_NN not null , trainer NUMBER(4) constraint O_TRAIN_FK references emp , location VARCHAR2(8) , constraint O_PK primary key (course,begindate) ) ; create table registrations ( attendee NUMBER(4) constraint R_ATT_NN not null constraint R_ATT_FK references emp , course VARCHAR2(6) constraint R_COURSE_NN not null , begindate DATE constraint R_BEGIN_NN not null , evaluation NUMBER(1) constraint R_EVAL_CHK check (evaluation in (1,2,3,4,5)) , constraint R_PK primary key (attendee,course,begindate) , constraint R_OFF_FK foreign key (course,begindate) references offerings ) ;