Oracle與DB2、MySQL取前10條記錄的對比

 

Oralce的示例：

1. 最佳選擇：利用分析函數

row_number() over ( partition by col1 order by col2 )
比如想取出100-150條記錄,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 虛列

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

註釋：使用序列時不能基於整個記錄集合來進行排序,假如指定了order by子句,排序的的是選出來的記錄集的排序。

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條不同id記錄，假如最後1條記錄的ID依然有相同的，那麼取出來。

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條記錄，假如第10條記錄的ID 還有相同的，那麼取出來。

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條記錄

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;

Db2示例

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 * 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) as tt where case1<=10

(1) 取前10條不同id記錄，假如最後1條記錄的ID依然有相同的，那麼全部取出來。

select * from mynumber where id in
(select distinct id from mynumber fetch first 10 rows only)

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) 
as 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) 
as tt where case1 between 5 and 10

(2)取前10條記錄，假如第10條記錄的ID 還有相同的，那麼全部取出來。

select * from mynumber where id in
(select id from mynumber fetch first 10 rows only)

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) 
as 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) 
as tt where case2 between 5 and 10

(3)取前10條記錄

select id from mynumber fetch first 10 rows only

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) as 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) 
as tt where case3 between 5 and 10

Mysql示例：

select id from mytable order by update_date desc limit 0,10

（責任編輯：盧兆林）