Multitable insert syntax support on Postgres?

Hi,

On 2022-11-14 21:06:09 -0300, Alexandre hadjinlian guerra wrote:

Hello
Are there any plans to incorporate a formal syntax multitable/conditional
insert , similar to the syntax below? snowflake does have the same feature

https://oracle-base.com/articles/9i/multitable-inserts

Today, im resorting to a function that receives the necessary parameters
from the attributes definition/selection area in a sql select query, called
by each tuple retrieved. A proper syntax show be real cool

I only skimmed that link, but afaict most of this can be done today in
postgres, with a bit different syntax, using CTEs. Postgres implements this as
an extension to the standard CTE syntax.

WITH data_src AS (SELECT * FROM source_tbl),
insert_a AS (INSERT INTO a SELECT * FROM data_src WHERE d < 5),
insert_b AS (INSERT INTO b SELECT * FROM data_src WHERE d >= 5)
INSERT INTO c SELECT * FROM data_src WHERE d < 5

It's a bit annoying that the last "arm" of the insert looks a bit
difference. OTOH, it's a much more general syntax.

Greetings,

Andres Freund

On Mon, Nov 14, 2022 at 7:06 PM Alexandre hadjinlian guerra <
alexhguerra@gmail.com> wrote:

Hello
Are there any plans to incorporate a formal syntax multitable/conditional
insert , similar to the syntax below? snowflake does have the same feature

https://oracle-base.com/articles/9i/multitable-inserts

Today, im resorting to a function that receives the necessary parameters
from the attributes definition/selection area in a sql select query, called
by each tuple retrieved. A proper syntax show be real cool

Thanks!

I'm not aware of any efforts to implement this at this time, mostly because
I don't think it's supported in the SQL Standard. Being in the standard
would change the question from "why" to "why not".

I've used that feature when I worked with Oracle in a data warehouse
situation. I found it most useful when migrating data dumps from mainframes
where the data file contained subrecords and in cases where one field in a
row changes the meaning of subsequent fields in the same row. That may
sound like a First Normal Form violation, and it is, but such data formats
are common in the IBM VSAM world, or at least they were in the data dumps
that I had to import.

WITH data_src AS (SELECT * FROM source_tbl),
insert_a AS (INSERT INTO a SELECT * FROM data_src WHERE d < 5),
insert_b AS (INSERT INTO b SELECT * FROM data_src WHERE d >= 5)
INSERT INTO c SELECT * FROM data_src WHERE d < 5

I suppose you could just do a dummy SELECT at the bottom to make it look
more symmetrical

WITH data_src AS (SELECT * FROM source_tbl),
insert_a AS (INSERT INTO a SELECT * FROM data_src WHERE d < 5),
insert_b AS (INSERT INTO b SELECT * FROM data_src WHERE d >= 5)
insert_c AS (INSERT INTO c SELECT * FROM data_src WHERE d < 5)
SELECT true AS inserts_complete;

Or maybe get some diagnostics out of it:

WITH data_src AS (SELECT * FROM source_tbl),
insert_a AS (INSERT INTO a SELECT * FROM data_src WHERE d < 5 RETURNING
NULL),
insert_b AS (INSERT INTO b SELECT * FROM data_src WHERE d >= 5 RETURNING
NULL),
insert_c AS (INSERT INTO c SELECT * FROM data_src WHERE d < 5 RETURNING
NULL)
SELECT
(SELECT COUNT(*) FROM insert_a) AS new_a_rows,
(SELECT COUNT(*) FROM insert_b) AS new_b_rows,
(SELECT COUNT(*) FROM insert_c) AS new_c_rows;