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From "Laura Stewart" <scotsmat...@gmail.com>
Subject Re: Need help on ORDER BY with expressions
Date Tue, 20 Feb 2007 22:23:57 GMT
I need some help understanding an example that was posted in DERBY-264.
The example is:

SELECT i, j FROM t ORDER BY f ( j )

I understand all but " f ".  Is that supposed to be "function"?

It would be better if I could see a real world example of using this
type of expression in the ORDER BY clause.

Thanks!
Laura

On 2/19/07, Laura Stewart <scotsmatrix@gmail.com> wrote:
> 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
>


-- 
Laura Stewart

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