Oracle rowITeye - 凯时娱乐

Oracle rowITeye

2019-01-12 12:54:26 | 作者: 迎丝 | 标签: 体育,函数,分页 | 浏览: 1997

原文地址:Oracle row_number() over()解析函数高效完成分页
create table T_NEWS
(
  ID  NUMBER,
  N_TYPE  VARCHAR2(20),
  N_TITLE VARCHAR2(30),
  N_COUNT NUMBER
)
;
prompt Disabling triggers for T_NEWS...
alter table T_NEWS disable all triggers;
prompt Loading T_NEWS...
insert into T_NEWS (ID, N_TYPE, N_TITLE, N_COUNT)
values (1, IT, 爱it1, 100);
insert into T_NEWS (ID, N_TYPE, N_TITLE, N_COUNT)
values (2, 体育, 爱体育1, 10);
insert into T_NEWS (ID, N_TYPE, N_TITLE, N_COUNT)
values (3, 体育, 爱体育2, 30);
insert into T_NEWS (ID, N_TYPE, N_TITLE, N_COUNT)
values (4, IT, 爱it2, 300);
insert into T_NEWS (ID, N_TYPE, N_TITLE, N_COUNT)
values (5, IT, 爱it3, 200);
insert into T_NEWS (ID, N_TYPE, N_TITLE, N_COUNT)
values (6, 体育, 爱体育3, 20);
insert into T_NEWS (ID, N_TYPE, N_TITLE, N_COUNT)
values (7, 体育, 爱体育4, 60);
commit;


第一步:我先用rownum

--分页 row_number,不是rownum
--依据n_count从大到小摆放,每页3条
SELECT ROWNUM r,t.* FROM t_news t
WHERE ROWNUM =3
ORDER BY t.n_count DESC
--问题:为什么order by今后,行号是乱的?
SELECT ROWNUM r,t.* FROM t_news t
--原因:先分配了行号,再依据n_count排序

--所以有必要排序,再生成行号
SELECT ROWNUM r,t.* FROM (
  SELECT t.* FROM t_news t ORDER BY t.n_count DESC  ) t

--分页
--err
SELECT ROWNUM r,t.* FROM (
  SELECT t.* FROM t_news t ORDER BY t.n_count DESC  ) t
WHERE r between 1 AND 3

--第1页
SELECT ROWNUM r,t.* FROM (
  SELECT t.* FROM t_news t ORDER BY t.n_count DESC  ) t
WHERE ROWNUM between 1 AND 3

--第2页
SELECT ROWNUM r,t.* FROM (
  SELECT t.* FROM t_news t ORDER BY t.n_count DESC  ) t
WHERE ROWNUM between 4 AND 6
--error: ROWNUM有必要从1开端!
SELECT k.* FROM (
SELECT ROWNUM r,t.* FROM (
  SELECT t.* FROM t_news t ORDER BY t.n_count DESC  ) t
) k
WHERE r BETWEEN 4 AND 6

--费事,功率低!


*****第二步:我用row_number() over()函数
select t2.* from
  (select t.*,row_number()over(order by t.n_count desc) orderNumber from t_news t order by t.n_count desc)t2 where orderNumber  between 1and 3;


*****************************************************************************************************************************************88
SELECT * FROM (
  SELECT  t.*,row_number() over(ORDER BY n_count DESC) r
  FROM t_news t
  ORDER BY t.n_count DESC
) t
WHERE r BETWEEN 4 AND 6

--通用语法: 解析函数() over(partition by 字段  order by 字段)
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