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From "Manish Khettry (JIRA)" <derby-...@db.apache.org>
Subject [jira] Commented: (DERBY-883) Enhance GROUP BY clause to support expressions instead of just column references.
Date Tue, 16 May 2006 00:59:07 GMT
    [ http://issues.apache.org/jira/browse/DERBY-883?page=comments#action_12402467 ] 

Manish Khettry commented on DERBY-883:
--------------------------------------

I have a few questions on this, largely functional.

1. In terms of syntax, do we allow expressions in the group by list or positional parameters,
or both?

select tomonth(creationdt), toyear(creationdt), count(*)
from bugs
group by 1, 2; 

or 
group by tomonth(creationdt), toyear(creationdt);

An implementation question on this note-- does the language code have a way of looking at
two expressions (ValueNode?) and checking to see if they are equivalent? We'll need some way
of doing this to match an expression in the group by list to an expression in the select list
right?

2. I assume that an expression in a group by list must appear in the select list without aggregation
right? Is this an error?

select x+1, x+2, sum(y)
from test
group by x
;

3. What do we do with duplicates? i.e.

select x+1, x+1, sum(y)
from test
group by x+1, x+1;

Is this an error? The current implementation throws an error if the same column occurs more
than once in the group by list.

Is there a standard somewhere which I should consult before trying to nail down the functionality?


> Enhance GROUP BY clause to support expressions instead of just column references.
> ---------------------------------------------------------------------------------
>
>          Key: DERBY-883
>          URL: http://issues.apache.org/jira/browse/DERBY-883
>      Project: Derby
>         Type: New Feature

>   Components: SQL
>     Versions: 10.1.2.1
>  Environment: JDK 1.5.0_05
>     Reporter: Lluis Turro
>     Assignee: Manish Khettry

>
> This select would return an error syntax on finding "(" after month if group by clause:
> select idissue, month(creation), year(creation), count(distinct idissue)
> where 
>   ....
> group by idissue, month(creation), year(creation)

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