Add constraint of cascade deleting
create table emp ( empno NUMBER(4) constraint E_PK primary key constraint E_EMPNO_CHK check (empno > 7000) , ename VARCHAR2(8) constraint E_NAME_NN not null , init VARCHAR2(5) constraint E_INIT_NN not null , job VARCHAR2(8) , mgr NUMBER(4) constraint E_MGR_FK references emp , bdate DATE constraint E_BDAT_NN not null , msal NUMBER(6,2) constraint E_MSAL_NN not null , comm NUMBER(6,2) , deptno NUMBER(2) default 10 , constraint E_SALES_CHK check (decode(job,'SALESREP',0,1) + nvl2(comm, 1,0) = 1) ) ; create table departments ( deptno NUMBER(2) constraint D_PK primary key constraint D_DEPTNO_CHK check (mod(deptno,10) = 0) , dname VARCHAR2(10) constraint D_DNAME_NN not null constraint D_DNAME_UN unique constraint D_DNAME_CHK check (dname = upper(dname)) , location VARCHAR2(8) constraint D_LOC_NN not null constraint D_LOC_CHK check (location = upper(location)) , mgr NUMBER(4) constraint D_MGR_FK references emp ) ; create table history ( empno NUMBER(4) constraint H_EMPNO_NN not null constraint H_EMPNO_FK references emp on delete cascade , beginyear NUMBER(4) constraint H_BYEAR_NN not null , begindate DATE constraint H_BDATE_NN not null , enddate DATE , deptno NUMBER(2) constraint H_DEPT_NN not null constraint H_DEPT_FK references departments , msal NUMBER(6,2) constraint H_MSAL_NN not null , comments VARCHAR2(60) , constraint H_PK primary key (empno,begindate) , constraint H_BEG_END check (begindate < enddate) ) ;