Re: CREATE TABLE AS, section IF NOT EXISTS should clarify what happens to the data

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От David G. Johnston
Тема Re: CREATE TABLE AS, section IF NOT EXISTS should clarify what happens to the data
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Msg-id CAKFQuwY30ro-xosyLZc=qFO3UhnudwvHO4oOJDqGawdQrtUWSA@mail.gmail.com
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Ответ на Re: CREATE TABLE AS, section IF NOT EXISTS should clarify what happens to the data  (Bruce Momjian <bruce@momjian.us>)
Ответы Re: CREATE TABLE AS, section IF NOT EXISTS should clarify what happens to the data  (Bruce Momjian <bruce@momjian.us>)
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On Thu, Jul 14, 2022 at 6:08 PM Bruce Momjian <bruce@momjian.us> wrote:
On Wed, Feb  9, 2022 at 01:02:51PM +0000, PG Doc comments form wrote:
> The following documentation comment has been logged on the website:
>
> Page: https://www.postgresql.org/docs/14/sql-createtableas.html
> Description:
>
> If I create a table with CREATE TABLE IF NOT EXISTS table_name AS, and the
> table exists already, I get a NOTICE instead of an ERROR.
>
> I wanted to have it clarified explicitly that the data from the SELECT
> statement is ignored in this case.

Good point.  Attached is a documentation patch to clarify this.


Not only is the existing table not modified, I think that the select query portion of the command is never even executed.  That would seem to be useful knowledge to have.

Maybe something like:

<para>
 Do not throw an error if a relation with the same name already exists.
 A notice is issued in this case.
 If <literal>WITH DATA</literal> is specified (the default) the execution of the parsed query does not happen, leaving the existing table with its existing contents.
</para>

I mention parsing since the command itself will fail if the query is invalid even if a table already exists.  But any potential runtime errors (or even side-effects) will not happen.

I've removed the xref to create table as there is nothing additional there of material benefit - the sentence:

"Note that there is no guarantee that the existing relation is anything like the one that would have been created."

is basically what we are adding here but this has more detail.

David J.

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