rownum

存在表T(a,b,c,d),要根据字段c排序后取第21—30条记录显示，请给出sql
    SELECT   *
        FROM (SELECT ROWNUM AS row_num, tmp_tab.*
                FROM (SELECT   a, b, c, d
                          FROM T
                      ORDER BY c) tmp_tab
               WHERE ROWNUM <= 30)
       WHERE row_num >= 20
ORDER BY row_num;

create table t(a number(,b number(,c number(,d number();
/
begin
for i in 1 .. 300 loop
insert into t values(mod(i,2),i/2,dbms_random.value(1,300),i/4);
end loop;
end;
/
select * from (select c.*,rownum as rn from (select * from t order by c desc) c) where rn between 21 and 30;
/
select * from (select * from test order by c desc) x where rownum &lt; 30
minus
select * from (select * from test order by c desc) y where rownum &lt; 20 order by 3 desc
相比之 minus性能较差