Thread: CREATE TABLE AS, section IF NOT EXISTS should clarify what happens to the data
CREATE TABLE AS, section IF NOT EXISTS should clarify what happens to the data
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PG Doc comments form
Date:
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.
Re: CREATE TABLE AS, section IF NOT EXISTS should clarify what happens to the data
From
Bruce Momjian
Date:
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. -- Bruce Momjian <bruce@momjian.us> https://momjian.us EDB https://enterprisedb.com Indecision is a decision. Inaction is an action. Mark Batterson
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Re: CREATE TABLE AS, section IF NOT EXISTS should clarify what happens to the data
From
"David G. Johnston"
Date:
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.
Re: CREATE TABLE AS, section IF NOT EXISTS should clarify what happens to the data
From
Bruce Momjian
Date:
fOn Thu, Jul 14, 2022 at 06:47:19PM -0700, David G. Johnston wrote: > 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 tried to go in that direction, but couldn't clearly name the SELECT/VALUES part of the CREATE TABLE AS query because CREATE TABLE AS is also a query. I felt trying to say we ran the CREATE TABLE AS query but not the SELECT/VALUES of the query was just too confusing. I used "simply issue a notice" as implying that nothing else happens, which I considered sufficient. > > I've removed the xref to create table as there is nothing additional there of > material benefit - the sentence: Okay, removed. Updated patch attached. -- Bruce Momjian <bruce@momjian.us> https://momjian.us EDB https://enterprisedb.com Indecision is a decision. Inaction is an action. Mark Batterson
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Re: CREATE TABLE AS, section IF NOT EXISTS should clarify what happens to the data
From
Bruce Momjian
Date:
On Mon, Jul 18, 2022 at 03:43:03PM -0400, Bruce Momjian wrote: > fOn Thu, Jul 14, 2022 at 06:47:19PM -0700, David G. Johnston wrote: > > 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 tried to go in that direction, but couldn't clearly name the > SELECT/VALUES part of the CREATE TABLE AS query because CREATE TABLE > AS is also a query. I felt trying to say we ran the CREATE TABLE AS > query but not the SELECT/VALUES of the query was just too confusing. I > used "simply issue a notice" as implying that nothing else happens, > which I considered sufficient. > > > > I've removed the xref to create table as there is nothing additional there of > > material benefit - the sentence: > > Okay, removed. Updated patch attached. Patch applied back to PG 10. -- Bruce Momjian <bruce@momjian.us> https://momjian.us EDB https://enterprisedb.com Indecision is a decision. Inaction is an action. Mark Batterson