On Thu, Mar 27, 2025 at 11:44 AM David G. Johnston <david.g.johns...@gmail.com> wrote: > > On Wednesday, March 26, 2025, Tom Lane <t...@sss.pgh.pa.us> wrote: >> >> jian he <jian.universal...@gmail.com> writes: >> > the attached patch is to implement $subject. >> >> Why would this be a good idea? I don't see any principled fallback >> definition of the column. (No, "NULL" is not that.) Certainly we >> should support ALTER TABLE DROP COLUMN, but removing the expression >> and not providing a substitute seems semantically nonsensical. > > > I don’t follow how NULL got involved in this discussion. The proposal is > basically: turn the virtual expression into an equivalent stored expression, > then drop the expression. > This discussion [0] wants to change stored to virtual.
drop the virtual generation, not materialize, column value will be NULL, but that will not work because commit [1] So we are either saying that virtual generation expression cannot be dropped, you can only substitute another expression or drop the expression, based on the dropped expression materializing that column value. [0]: https://postgr.es/m/CAFCRh-8grTkEy%2B73q79iXB%2Bq%2BsD%3DQkbz-vNAN1KJCF6PRLa%3Dzg%40mail.gmail.com [1]: https://git.postgresql.org/cgit/postgresql.git/commit/?id=cdc168ad4b22ea4183f966688b245cabb5935d1f
