Horton

Re: Virtual generated columns

Peter Eisentraut <peter@eisentraut.org>

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From: Peter Eisentraut <peter@eisentraut.org>
To: Richard Guo <guofenglinux@gmail.com>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>, jian he <jian.universality@gmail.com>, Dean Rasheed <dean.a.rasheed@gmail.com>
Date: 2025-01-08T13:41:50Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Expand virtual generated columns for ALTER COLUMN TYPE

  2. Eliminate code duplication in replace_rte_variables callbacks

  3. Expand virtual generated columns in the planner

  4. Virtual generated columns

  5. Additional tests for stored generated columns

  6. Improve generated_stored test

  7. Fix handling of CREATE DOMAIN with GENERATED constraint syntax

  8. Add pg_constraint rows for not-null constraints

  9. Put generated_stored test objects in a schema

  10. Rename regress test generated to generated_stored

  11. Small code simplification

  12. Remove useless code

  13. Remove useless initializations

  14. doc: Clarify that pg_attrdef also stores generation expressions

  15. Clean out column-level pg_init_privs entries when dropping tables.

  16. Re-implement the ereport() macro using __VA_ARGS__.

On 08.01.25 09:22, Richard Guo wrote:
>> - Added support for ALTER TABLE ... SET EXPRESSION.
> When using ALTER TABLE to set expression for virtual generated
> columns, we don't enforce a rewrite, which means we don't have the
> opportunity to check whether the new values for these columns could
> cause an underflow or overflow.  For instance,
> 
> create table t (a int, b int generated always as (a) virtual);
> insert into t values (2147483647);
> 
> # alter table t alter column b set expression as (a * 2);
> ALTER TABLE
> 
> # select * from t;
> ERROR:  integer out of range
> 
> The same thing could occur with INSERT.  As we don't compute virtual
> generated columns on write, we may end up inserting values that cause
> underflow or overflow for these columns.
> 
> create table t1 (a int, b int generated always as (a * 2) virtual);
> insert into t1 values (2147483647);
> 
> # select * from t1;
> ERROR:  integer out of range
> 
> I'm not sure if this is expected or not, so I just wanted to point it
> out.

Yes, this is expected behavior.  This also happens with a view.  So it 
is consistent for compute-on-read objects.