Re: support ALTER COLUMN SET EXPRESSION over virtual generated column with check constraint

On Sat, Jan 17, 2026 at 12:07 AM Matheus Alcantara
<matheusssilv97(at)gmail(dot)com> wrote:
>
> >
> > <varlistentry id="sql-altertable-desc-set-expression">
> > <term><literal>SET EXPRESSION AS</literal></term>
> > <listitem>
> > <para>
> > This form replaces the expression of a generated column. Existing data
> > in a stored generated column is rewritten and all the future changes
> > will apply the new generation expression.
> > + Virtual generated columns do not require a table rewrite.
> > + However if the column is part of a <literal>CHECK</literal> constraint
> > + expression, the constraint will be rebuilt, requiring a table scan to
> > + ensure that existing rows meet the constraint.
> > </para>
>
> Sounds good.
>

hi.

I ultimately settled on the following:
+ Replacing the expression of a virtual generated columns do not require a
+ table rewrite, however if the column is part of a
<literal>CHECK</literal>
+ constraint expression, the constraint will be rebuilt, requiring a table
+ scan to ensure that existing rows meet the constraint.

--
jian
https://www.enterprisedb.com