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From <de...@segel.com>
Subject RE: How to emulate multiple DISTINCT aggregates?
Date Mon, 28 Aug 2006 21:49:50 GMT
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 query?

 

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:

 


1

 1

 1


2

 2

 2


1

 1

 3

 

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

 

This one works:

 

SELECT 
(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
FROM SYSIBM.SYSDUMMY1

 

Regards,

Ali


derby@segel.com wrote:


Hi,

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? 

-G

> -----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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