Thread: ALTER TABLE atomicity with sub-commands

The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/15/sql-altertable.html
Description:

Hello dear PostgreSQL family,

It is not entirely clear (to me) that ALTER TABLE statements with
comma-separated sub-commands are atomic. Despite of saying "perform X
actions in one operation" in one of the examples, it is not explicitly said
that the operation will be rolled back if one of the sub-commands fails. 

From the examples, we have:

ALTER TABLE distributors
    ALTER COLUMN address TYPE varchar(80),
    ALTER COLUMN name TYPE varchar(100);

Will the `address` column type change rollback if the `ALTER COLUMN name
TYPE varchar(100)` subcommand fails?

Currently reading the docs for version 15.

Many thanks :)

On 2024-04-02 16:40 +0200, PG Doc comments form wrote:
> The following documentation comment has been logged on the website:
> 
> Page: https://www.postgresql.org/docs/15/sql-altertable.html
> Description:
> 
> It is not entirely clear (to me) that ALTER TABLE statements with
> comma-separated sub-commands are atomic. Despite of saying "perform X
> actions in one operation" in one of the examples, it is not explicitly said
> that the operation will be rolled back if one of the sub-commands fails. 
> 
> From the examples, we have:
> 
> ALTER TABLE distributors
>     ALTER COLUMN address TYPE varchar(80),
>     ALTER COLUMN name TYPE varchar(100);
> 
> Will the `address` column type change rollback if the `ALTER COLUMN name
> TYPE varchar(100)` subcommand fails?
> 
> Currently reading the docs for version 15.

Yes, ALTER TABLE, like all statements, is one atomic change.

From BEGIN[1]:

    By default (without BEGIN), PostgreSQL executes transactions in
    “autocommit” mode, that is, each statement is executed in its own
    transaction and a commit is implicitly performed at the end of the
    statement (if execution was successful, otherwise a rollback is
    done).

[1] https://www.postgresql.org/docs/15/sql-begin.html

-- 
Erik