Обсуждение: SQL query (general)

i have the following table  R
id    a1    a2
1    A    B
2    A    B
3    B    C
4    C    A
5    B     C

and to write  q uery thats outputs the following
id    a1    a2
1    A    B
2    A    B
3    B    C
5    B    C

Is the following query correct?
select *
from  (select *       from R       groupby a1) as T1,   (select *       from R       groupby a1) as T2,
where T1.id<>T2.id
AND T1.a1=T2.a1
AND T1.a2=T2.a2;

please correct.

Why don't you write in words what you are trying to accomplish.
To me, it looks like the query should be:

select * from R where a2 > a1;




D'laila Pereira wrote:
> 
> i have the following table  R
> id    a1    a2
> 1    A    B
> 2    A    B
> 3    B    C
> 4    C    A
> 5    B     C
> 
> and to write  q uery thats outputs the following
> id    a1    a2
> 1    A    B
> 2    A    B
> 3    B    C
> 5    B    C
> 
> Is the following query correct?
> select *
> from  (select *
>         from R
>         groupby a1) as T1,
>     (select *
>         from R
>         groupby a1) as T2,
> where T1.id<>T2.id
> AND T1.a1=T2.a1
> AND T1.a2=T2.a2;
> 
> please correct.
> 
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