Oracle row_number() over()解析函数高效达成分页
发布时间：2021-11-27 09:21:37 所属栏目：教程 来源：互联网
导读：复制代码 代码如下: 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 (I
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复制代码 代码如下: 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 --根据n_count从大到小排列，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以后，行号是乱的？ SELECT ROWNUM r,t.* FROM t_news t --原因：先分配了行号，再根据n_count排序 --所以必须排序，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必须从1开始！ 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 --麻烦，效率低！ *****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)  （编辑：沧州站长网） 【声明】本站内容均来自网络，其相关言论仅代表作者个人观点，不代表本站立场。若无意侵犯到您的权利，请及时与联系站长删除相关内容! |
