SQL UNION 和 UNION ALL 操作符的实例

UNION ALL中的实例解析

写一SQL语句，从表EMP中查询出所有员工的工资，工资最高的的三个员工排在最前面并按工资字段升序排序，其余记录正常查询出来放在后面。

select * from (select *  from emp  where empno  in (                            select empno                       from (select A.*, rownum                                from (select * from emp order by sal desc)A                               order by sal desc)                      where rownum < 4                  )  order by sal                  )      union all select *  from emp  where empno not in (                            select empno                       from (select A.*, rownum                                from (select * from emp order by sal desc)A                               order by sal desc)                      where rownum < 4);