The following article mainly describes the actual comparison between the Oracle database and DB2 and MySQL with the first 10 records. The following article mainly uses Oralce as an example to explain their differences, the following is a detailed description of the article. I hope you will get some benefits.
1. Best Choice: use analysis functions
- row_number() over ( partition by col1 order by col2 )
For example, if you want to retrieve-records, sort them by tname.
- select tname,tabtype from (
- select tname,tabtype,row_number() over ( order by tname ) rn from tab
- )
- where rn between 100 and 150;
2. Use rownum virtual
- select tname,tabtype from (
- select tname,tabtype,rownum rn from tab where rownum <= 150
- )
- where rn >= 100;
Note: sequence sorting cannot be performed based on the entire set of records. If the order by clause is specified, the sorting of the selected set of records is used.
- 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) the comparison between Oracle database and DB2 and MySQL requires the first 10 different id records. If the IDs of the last record are still the same, then, it is retrieved.
- 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) obtain the first 10 records. If the IDs of the first 10 records are the same, obtain them.
- 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) obtain the first 10 records
- 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;
The above content is an introduction to the comparison between the Oracle database and DB2 and MySQL with the first 10 records. I hope you will have some gains.
Article by: http://www.programbbs.com/doc/class10-1.htm