haskelldb-users

[Haskelldb-users] About unique

[Guenther S. <gue...@we...>]

Hi guys,

I can honestly say that I don't have a clue on how to use it. Or rather 
where to place it. Or rather to use it to actually get a "select  
distinct".
Whenever I did use it, it always grouped at the innermost level.
How can you determine the level *where* the grouping takes place?

Günther

Re: [Haskelldb-users] About unique

[Justin B. <jgb...@gm...>]

If you want select distinct, "unique" won't give it. The library does
that through Group By instead. Can you be more specific?

On Fri, May 1, 2009 at 10:04 AM, Guenther Schmidt <gue...@we...> wrote:
> Hi guys,
>
> I can honestly say that I don't have a clue on how to use it. Or rather
> where to place it. Or rather to use it to actually get a "select
> distinct".
> Whenever I did use it, it always grouped at the innermost level.
> How can you determine the level *where* the grouping takes place?
>
> Günther
>
>
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Re: [Haskelldb-users] About unique

[Guenther S. <gue...@we...>]

Hi Justin,


this is really very frustrating: Every time I think I spotted a bug, a 
flaw, or a deficiency it just turns out to be a mistake in my thinking!

This thing is perfect, apparently, awesome, great, wonderful!

It certainly saved my ass with this project.

Thanks for pointing out subQuery, I hadn't come across that one yet.

Many, many thanks

Günther



Justin Bailey schrieb:
> I came up with this SQL to represent what you want:
>
>   select col1, count(col2)
>   from (select col1, col2
>            from table1
>            group by col1, col2)
>   group by col1
>
> You need to use the "subQuery" operator:
>
>   query = do
>     inner <- subQuery $ do
>       t1 <- table table1
>       unique
>       project $ table1 ! col1 << col1,
>                     table1 ! col2 << col2
>     project $ t1 ! col1 << col1 #
>                  t2 ! col2 << count(col2)
>
> I think that would do it. Did you figure it out?
>
> On Fri, May 1, 2009 at 10:41 AM, Guenther Schmidt <gue...@we...> wrote:
>   
>> Hi Justin,
>>
>> lets say in the inner query I select 2 columns. There will be some
>> duplicates due to identical value pairs in cols 1 & 2.
>>
>> I will eventually only select col 1 and the count of *distinct* pairs of col
>> 1 & 2.
>>
>> Using:
>>
>>   select col1, count (col2) ...   naturally includes the duplicates, which I
>> don't want.
>>
>> How can I do that?
>>
>> Günther
>>
>>
>>
>>