Oracle数据库和DB2取前10条记录的实际对比
以下的文章主要讲述的是Oracle数据库和DB2、MySQL取前10条记录的实际对比，以下的文章主要以Oralce为示例来讲解它们的不同，以下就是文章的详细内容介绍，希望大家能有所收获。
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1. ***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
- select tname,tabtype from (
- select tname,tabtype,rownum rn from tab where rownum <= 150
- )
- where rn >= 100;
注释：使用序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)Oracle数据库与DB2、MySQL取前10条记录的对比要取前10条不同id记录，假如***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;
以上的相关内容就是对Oracle数据库与DB2、MySQL取前10条记录的对比的介绍，望你能有所收获。
文章出自:http://www.programbbs.com/doc/class10-1.htm
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