Re: ALTER COLUMN ... SET EXPRESSION to alter stored generated column's expression

On Mon, Nov 13, 2023 at 9:09 PM Peter Eisentraut <peter(at)eisentraut(dot)org>
wrote:

> On 13.11.23 14:07, Amul Sul wrote:
> > Also, it seems to me that the SET EXPRESSION variant should just do
> an
> > update of the catalog table instead of a drop and re-insert.
> >
> > I am not sure if that is sufficient; we need to get rid of the
> > dependencies of
> > existing expressions on other columns and/or objects that need to be
> > removed.
> > The drop and re-insert does that easily.
>
> Ok, good point.
>
> > The documentation needs some improvements:
> >
> > + ALTER [ COLUMN ] <replaceable
> > class="parameter">column_name</replaceable> SET EXPRESSION
> <replaceable
> > class="parameter">expression</replaceable> STORED
> >
> > If we're going to follow the Db2 syntax, there should be an "AS"
> after
> > EXPRESSION. And the implemented syntax requires parentheses, so they
> > should appear in the documentation.
> >
> > Also, the keyword STORED shouldn't be there. (The same command
> should
> > be applicable to virtual generated columns in the future.)
> >
> > I have omitted "AS" intentionally, to keep syntax similar to our existing
> > ALTERCOLUMN... SET DEFAULT <a_expr>. Let me know if you want
> > me to add that.
>
> Well, my idea was to follow the Db2 syntax. Otherwise, we are adding
> yet another slightly different syntax to the world. Even if we think
> our idea is slightly better, it doesn't seem worth it.
>

Ok.

Please have a look at the attached version, updating the syntax to have "AS"
after EXPRESSION and other changes suggested previously.

Regards,
Amul