Re: Converting SQL Server Top N to Oracle Equivalent
- From: dcosta@xxxxxxx
- To: mkb125@xxxxxxxxx
- Date: Thu, 23 Oct 2008 10:12:41 +0100 (WEST)
Hello,
In the following example You will see You are right:
Your query will retrieve the right set of data.
create table ALG
(change_id number(2),
type varchar2(5),
time_stamp date);
create table CHG
(id number(2),
type varchar2(5),
time_stamp date);
delete from ALG;
insert into ALG values(1, 'CL', sysdate);
insert into ALG values(2, 'RE', sysdate+1);
insert into ALG values(3, 'CL', sysdate+2);
insert into ALG values(4, 'RE', sysdate+3);
insert into ALG values(5, 'CL', sysdate-1);
insert into ALG values(6, 'RE', sysdate-2);
insert into ALG values(7, 'RE', sysdate-5);
insert into ALG values(8, 'CL', sysdate+9);
insert into ALG values(9, 'RE', sysdate-8);
delete from CHG;
insert into CHG values(1, 'CL', sysdate-6);
insert into CHG values(2, 'RE', sysdate+1);
insert into CHG values(3, 'CL', sysdate-8);
insert into CHG values(14, 'RE', sysdate+9);
insert into CHG values(15, 'CL', sysdate-4);
insert into CHG values(61, 'RE', sysdate-1);
insert into CHG values(71, 'RE', sysdate+2);
insert into CHG values(18, 'CL', sysdate+3);
insert into CHG values(91, 'RE', sysdate+11);
-- I considered the existence of a type column in the CHG table
-- causing small change in Your query in the references to avoid
-- the ambiguity: "and (ALG.type = 'CL' or ALG.type = 'RE') "
-- If You comment the restriction "where rownum <= 1"
select b.time_stamp
from (
select alg.time_stamp
from ALG, CHG
where ALG.change_id = CHG.id
and (ALG.type = 'CL' or ALG.type = 'RE')
order by ALG.time_stamp asc) b
--where rownum <= 1
order by rownum asc
/
-- the result will be the following:
TIME_STA
--------
08.10.23
08.10.24
08.10.25
-- If You maintain the restriction
select b.time_stamp
from (
select alg.time_stamp
from ALG, CHG
where ALG.change_id = CHG.id
and (ALG.type = 'CL' or ALG.type = 'RE')
order by ALG.time_stamp asc) b
where rownum <= 1
order by rownum asc
/
-- the result will be the one You want: the first line in the set will
-- make the result set
TIME_STA
--------
08.10.23
drop table ALG;
drop table CHG;
Best regards
Dias Costa
> Hi,
>
> Gota SS2K5 query that I'm trying to convert over to Oracle 10gR2.
>
> This is the SS2K5 query:
>
> select top 1 ALG.time_stamp
> from ALG, CHG
> where ALG.change_id = CHG.id
> and (type = 'CL' or type = 'RE')
> order by ALG.time_stamp ASC
>
> I coded the Oracle 10gR2 equivalent as follows:
>
> select b.time_stamp
> from (
> select alg.time_stamp
> from ALG, CHG
> where ALG.change_id = CHG.id
> and (type = 'CL' or type = 'RE')
> order by ALG.time_stamp asc) b
> where rownum <= 1
> order by rownum asc
> /
>
> Is this the correct way to do it? I wish I could check the results
> between the SS2K5 db and the Oracle db but I don't have access to the SS
> db and even if I did, the data sets are very different.
>
> Anyway, just wanted to know if I was on the right track or am I totally
> off-base here.
>
> tia
>
> --
> mohammed
>
>
>
> --
> //www.freelists.org/webpage/oracle-l
>
>
>
--
//www.freelists.org/webpage/oracle-l
Other related posts:
