Re: Why cannot alter a column's type when it's used by a generated column

> On Oct 21, 2025, at 15:30, jian he <jian.universality@gmail.com> wrote:
> 
> +-- So, you can change a column's type as long as any dependent generated
> +-- column already has a set expression defined:
> +ALTER TABLE gtest27
> +  ALTER COLUMN a TYPE float8,
> +  ALTER COLUMN x SET EXPRESSION AS ((a::int + b) * 2);
> +\d gtest27
> +                                Table "generated_stored_tests.gtest27"
> + Column |       Type       | Collation | Nullable |
>   Default
> +--------+------------------+-----------+----------+---------------------------------------------------
> + a      | double precision |           |          |
> + b      | bigint           |           |          |
> + x      | bigint           |           |          | generated always
> as ((a::integer + b) * 2) stored
> +
> 
> the above output seems wrong?
> one way to quickly test it is create table  gtest27 again

I don’t get what is wrong? Actually “make check” passed from my side:

```
% make check
…
1..230
# All 230 tests passed.
```

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/