select *
from
(select * from (select t.*, rownum linenum from gal_messages t) r where r.linenum <200) a
where a.linenum>100
Note: 一定要给rownum一个别名linenum, 否则r.rownum或a.rownum会出错.
Oracle Connect By用法
参照:[url]http://www.cublog.cn/u1/54706/showart_1711812.html
oracle中的select语句可以用START WITH...CONNECT BY PRIOR子句实现递归查询,connect by 是结构化查询中用到的,其基本语法是:
select ... from <TableName>
where <Conditional-1>
start with <Conditional-2>
connect by <Conditional-3>
;
<Conditional-1>:过滤条件,用于对返回的所有记录进行过滤。
<Conditional-2>:查询结果重起始根结点的限定条件。
<Conditional-3>:连接条件
数据库表结构如下:
create table t2(
root_id number,
id number,
name varchar(5),
description varchar(10)
);
insert into t2(root_id,id,name,description) values(0,1,'a','aaa');
insert into t2(root_id,id,name,description) values(1,2,'a1','aaa1');
insert into t2(root_id,id,name,description) values(1,3,'a2','aaa2');
insert into t2(root_id,id,name,description) values(0,4,'b','bbb');
insert into t2(root_id,id,name,description) values(4,5,'b1','bbb1');
insert into t2(root_id,id,name,description) values(4,6,'b2','bbb2');
获取完整树:
select * from t2 start with root_id = 0 connect by prior id = root_id;
查询结果: 所有记录
获取特定子树:
select * from t2 start with id = 1 connect by prior id = root_id;
查询结果:
root_id id
0 1
1 2
1 3
select * from t2 start with id = 4 connect by prior id = root_id;
root_id id
0 4
4 5
4 6
如果connect by prior中的prior被省略,则查询将不进行深层递归。
For example:
select * from t2 start with root_id = 0 connect by id = root_id;
root_id id
0 1
0 4
select * from t2 start with id = 1 connect by id = root_id;
root_id id
0 1