Oracle 伪列、取前几条记录、日期判断等

从表中随机取4条记录：

select * from (select * from 表 order by dbms_random.random) where rownum < 5


伪列2type：

select * from (
select ai.activityId,ai.owner,ai.creatorName, ai.subject,ai.createDate,2type
from ActivityInfo ai
union
select aj.activityId,aj.joinId as owner,aj.joinName as creatorName, ai.subject,aj.attendDate as createDate,aj.type from ActivityJoin aj
INNER JOIN ActivityInfo ai ON aj.activityId=ai.activityId
order by createDate desc
)
where rownum < 5


日期：
(1)
string dateTo = DateTime.Now.AddDays(-1).ToShortDateString();
dateTo = "to_date('" + dateTo + "','yyyy-mm-dd') ";
string dateFrom = DateTime.Now.AddDays(1).ToShortDateString();
dateFrom = "to_date('" + dateFrom + "','yyyy-mm-dd') ";
sql += " and f.DateFrom < " + dateFrom + " and f.DateTo > " + dateTo;

(2)
update 表set 字段=to_date('2010-2-17 14:36:27','yyyy-mm-dd hh24:mi:ss')
where name='abc88'

系统GUID：sys_guid()
系统日期：sysdate

pl/sql导出表结构:

Tools-->Export User Objects -->选择要导出的表-->.sql文件

pl/sql导出表数据:

Tools-->Export Tables-->选择表,选择SQL Inserts-->.sql文件