Oracle 中 rownum的用法

http://www.oracle.com/technology/oramag/oracle/06-sep/o56asktom.html

 

Consider a query with this structure:

 

select ..., ROWNUM
  from t
 where <where clause>
 group by <columns>
having <having clause>
 order by <columns>;

Think of it as being processed in this order:

1. The FROM/WHERE clause goes first.
2. ROWNUM is assigned and incremented to each output row from the FROM/WHERE clause.
3. SELECT is applied.
4. GROUP BY is applied.
5. HAVING is applied.
6. ORDER BY is applied.

 

 

建表

create table t as select mod(level,5) id, trunc(dbms_random.value(1,100)) data from dual connect by level <= 100;

 

查询第40条到50条

select * from (select a.*, rownum rnum from (select id, data from t order by id) a where rownum <= 50) where rnum >= 40;