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From Suavi Ali Demir <dem...@yahoo.com>
Subject RE: How to emulate multiple DISTINCT aggregates?
Date Tue, 29 Aug 2006 02:45:23 GMT
Let's look at the query differently to see what it is trying to say:
  SELECT  count(some columns) FROM table_a a
WHERE ( some field1 criteria thats always true )
AND ( some field2 criteria thats always true )
AND (some field3 criteria thats always true )

  The where clause will always be true. For a given row, if where clause is true, the tuples
of that row will be returned. That would make 3 rows (all rows) returned in this case since
where clause is always true. And which column we count does not matter i guess. 

derby@segel.com wrote:
        v\:* {behavior:url(#default#VML);}  o\:* {behavior:url(#default#VML);}  w\:* {behavior:url(#default#VML);}
 .shape {behavior:url(#default#VML);}        st1\:*{behavior:url(#default#ieooui) }      
         That doesn’t make sense.
  Each sub select statement should have returned the following
  Field A {1,2}
  Field B {1,2}
  Field C {1,2,3}
  Then in the original select, your counts should be {2,2,3};
  Note: I used Informix. 
  There is something interesting going on. You’re using a dummy table as a wrapper for 3.
  Now I wonder what the optimizer thinks of this and how, if at all, does it parallelize the
  I’ll try my sql method on a similar table to yours, but I do think the response you saw
wasn’t correct.
  From: Suavi Ali Demir [mailto:demir4@yahoo.com] 
Sent: Monday, August 28, 2006 3:52 PM
To: Derby Discussion; msegel@segel.com
Subject: RE: How to emulate multiple DISTINCT aggregates?

    That query needs to be modified little bit. It does not work when

    my table contains:




    result is 3,3,3, where as it should have been 2,2,3.


    This one works:


(SELECT COUNT(DISTINCT b.field1) FROM table_a b) as field1_count, 
(SELECT COUNT(DISTINCT c.field2) FROM table_a c) as field2_count, 
(SELECT COUNT(DISTINCT d.field3) FROM table_a d) as field3_count




derby@segel.com wrote:


Uhm you can't do what you want to do as written....

When you say SELECT COUNT(DISTINCT blah), it has to be unique to your query.
So no multiple COUNT(DISTINCTS xxx) allowed in a single query.
However here's a work around that may help...

SELECT COUNT(a.field1), COUNT(a.field2), COUNT(a.field3) ...
FROM table_a a
WHERE a.field1 in ( SELECT DISTINCT b.field1 FROM table_a b)
AND a.field2 in ( SELECT DISTINCT b.field2 FROM table_a b)
AND a.field3 in ( SELECT DISTINCT b.field3 FROM table_a b)

Well you get the idea.

It's then pretty straight forward.
Each subselect returns the distinct set of elements and then your outer
select returns the count on these unique subsets.

I just tried it in Informix (I happen to have a table with a couple of
string columns of data that I am working on.)
Should work in Derby. Its all standard SQL

But Hey! What do I know? 


> -----Original Message-----
> From: Robert Enyedi [mailto:robert.enyedi@intland.com]
> Sent: Monday, August 28, 2006 10:58 AM
> To: Derby Discussion
> Subject: How to emulate multiple DISTINCT aggregates?
> Hi,
> When trying to use multiple DISTINCT aggregates in Derby:
> /SELECT COUNT(distinct editable), COUNT( distinct visible )
> FROM item/
> the following error is reported:
> /ERROR 42Z02: Multiple DISTINCT aggregates are not supported at this
> time./
> For a simple query one could write:
> /SELECT COUNT(distinct editable) AS editable_count, COUNT( (SELECT
> DISTINCT visible FROM item) )
> FROM item/
> but this is actually pretty uncomfortable and unmaintainable in a larger
> query.
> Does anyone know an elegant overcome for this Derby limitation?
> Thanks,
> Robert


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