create table a_111111_b ( a varchar2(100), b varchar2(100), c varchar2(100), d varchar2(100), e varchar2(100));
alter table a_111111_b add constraint PK_a_111111_b primary key (a, b);
复合主键
原文：http://www.cnblogs.com/zhangwensi/p/4892148.html
