Re: Converting SQL Server Top N to Oracle Equivalent

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
>
>
>
> --
> http://www.freelists.org/webpage/oracle-l
>
>
>


--
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