摘要： 集合操作符UNION/UNION ALLINTERSECTMINUSUnion All不排序，不去重，其余均升序且去重。create table e1 as select * from emp where deptno in (10,20);create table e2 as select * from emp where deptno in (20,30);select * from e1 union select * from e2 order by 8select * from e1 union all select * from e2 order by 8select * from 阅读全文