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  • Oracle查前几条记录方法

    Oralce的示例:

    1. 最佳选择:利用分析函数

           row_number() over ( partition by col1 order by col2 )
                                   比如想取出100-150条记录,按照tname排序

                   select tname,tabtype from (
                                   select tname,tabtype,row_number() over ( order by tname ) rn from tab
                    ) where rn between 100 and 150;

    2. 使用rownum 虚列

             select tname,tabtype from (
                        select tname,tabtype,rownum rn from tab where rownum <= 150
                      ) where rn >= 100;

    注释:使用虚列时不能基于整个记录集合来进行排序,假如指定了order by子句,排序的是选出来的记录集的排序 create table mynumber(id int,name varchar(10));
             insert into mynumber values(1,'no1');
             insert into mynumber values(2,'no2');
             insert into mynumber values(3,'no3');
            insert into mynumber values(4,'no4');
            insert into mynumber values(5,'no5');
            insert into mynumber values(5,'no6');
            insert into mynumber values(6,'no7');
            insert into mynumber values(7,'no8');
            insert into mynumber values(8,'no9');
            insert into mynumber values(9,'no10');
            insert into mynumber values(9,'no11');
            insert into mynumber values(9,'no12');
            insert into mynumber values(10,'no13');
            insert into mynumber values(10,'no14');
            insert into mynumber values(10,'no15');
            insert into mynumber values(11,'no16');
            insert into mynumber values(12,'no17');
            insert into mynumber values(13,'no18');

         select id,name,RANK() over ( order by id ) case1,
                DENSE_RANK() over ( order by id ) case2,
                row_number() over ( order by id ) case3 from mynumber;

       

    (1) 取前10条不同id记录,假如最后1条记录的ID依然有相同的,那么取出来

       select id,name from mynumber where id in
             (select id from (select distinct id
              from mynumber) tt where rownum<=10);

               select * from (select id,name,RANK()
               over ( order by id ) case1,DENSE_RANK()
               over ( order by id ) case2,row_number()
                over ( order by id ) case3 from mynumber)
                tt where case1<=10;
              select * from (select id,name,RANK() over
              ( order by id ) case1,DENSE_RANK() over
              ( order by id ) case2,row_number() over
              ( order by id ) case3 from mynumber)
               tt where case1 between 5 and 10;

       (2)取前10条记录,假如第10条记录的ID 还有相同的,那么取出来

       select * from mynumber where id in
               (select id from mynumber where rownum <=10);

                select * from (select id,name,RANK()
                over ( order by id ) case1,DENSE_RANK()
                over ( order by id ) case2,row_number()
                over ( order by id ) case3 from mynumber)
                tt where case2<=10;
                select * from (select id,name,RANK()
                 over ( order by id ) case1,DENSE_RANK()
                over ( order by id ) case2,row_number()
                over ( order by id ) case3 from mynumber)
                tt where case2 between 5 and 10;

    (3)取前10条记录

           select id,name from mynumber
                  where rownum <=10;
                   select id,name from
                  (select id,name,rownum rn from
                    mynumber where rownum <= 10 ) where rn >= 5;

                  select * from (select id,name,RANK()
                  over ( order by id ) case1,DENSE_RANK()
                   over ( order by id ) case2,row_number()
                  over ( order by id ) case3 from mynumber)
                  tt where case3<=10;
                  select * from (select id,name,RANK()
                  over ( order by id ) case1,DENSE_RANK()
                  over ( order by id ) case2,row_number()
                  over ( order by id ) case3 from mynumber)
                   tt where case3 between 5 and 10;

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  • 原文地址:https://www.cnblogs.com/emanlee/p/2153662.html
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