Add constraints for value in a constant list
create table courses ( code VARCHAR2(6) constraint C_PK primary key , description VARCHAR2(30) constraint C_DESC_NN not null , category CHAR(3) constraint C_CAT_NN not null , duration NUMBER(2) constraint C_DUR_NN not null , constraint C_CODE_CHK check (code = upper(code)) , constraint C_CAT_CHK check (category in ('GEN','BLD','DSG')) ) ;