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From "Laura Stewart" <scotsmat...@gmail.com>
Subject Re: Need help on ORDER BY with expressions
Date Tue, 20 Feb 2007 01:25:20 GMT
Thanks Yip, this helped alot.  I will be posting a patch for DERBY-264
very soon.
I'd appreciate it if you could take a look.  Especially at the examples...

Laura

On 2/19/07, Yip Ng <yipng168@gmail.com> wrote:
> On 2/16/07, Laura Stewart <scotsmatrix@gmail.com> wrote:
>
> > 1. The type of expressions that are allowed. My impression is that
> > they are the Boolean expressions (as opposed to TableExpressions or
> > SelectExpressions)?
>
> ORDER BY expression is not limited to boolean expression only.  It can contain
> common value expression such as numeric, string, datetime, etc.  It can also
> have row value expression such as a scalar subquery, case expression, etc.
>
>
> > 2. I need to understand how the Syntax for ORDER BY should appear.
> > Should it just be "Expressions" added immediately after ColumnPosition
> > (in both places in the Syntax? Or should it be specific type of
> > expression (TableExpression, SelectExpression, Boolean Expression).
> > Are there limitations as to the types of expressions allowed? Boolean,
> > concatenation?
>
> Perhaps the name sort-key expression would be more appropriate?
> Adding it after Column Position is fine.
>
> > 3. Description of the expressions allowed (will appear below the
> > syntax) This will depend on what type of expressions are allowed, but
> > one thing that the other parameters mention is if the column needs to
> > be in the select list. I need help describing the expressions
> > parameter.
>
>
> > 4. Whatever type of expressions are allowed, that topic in the Derby
> > Ref Guide needs to be updated too. Are there any limitations for ORDER
> > BY? For example, the Boolean expressions topic mentions that there are
> > limitations with check constraints.
> >
>
> Yes, there are restrictions.  If SELECT DISTINCT is specified or the
> SELECT statement contains a GROUP BY clause, the ORDER BY columns need
> to appear in the SELECT list.
>
> I think there is a bug in Derby in the DISTINCT with ORDER BY case and
> I have filed a jira for this.  See DERBY-2351 for further details.
>
> Hope this helps.
>
> Regards,
> Yip Ng
>


-- 
Laura Stewart

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