Re: RE: [GENERAL] INSERT. RETURNING for copying records

 

From: pgsql-general-owner@postgresql.org [mailto:pgsql-general-owner@postgresql.org] On Behalf Of Michael Sacket
Sent: Friday, September 07, 2012 2:09 PM
To: PG-General Mailing List
Subject: [GENERAL] INSERT… RETURNING for copying records

 

Good Afternoon,

 

I'm attempting to write a function that will duplicate a few records, but the catch is I need to have a mapping of the original pk to the new pk.  I know I can use the RETURNING clause to get the new ids... but how to map that to the original ones is escaping me.

 

< Setup >

 

CREATE TABLE testing (rid serial PRIMARY KEY, category text NOT NULL, name text NOT NULL, fk_parent int4);

 

INSERT INTO testing (category, name, fk_parent) VALUES ('cat1', 'one', NULL), ('cat1', 'one.one', 1), ('cat1', 'one.two', 1);

 

SELECT * FROM testing;
+-----+----------+---------+-----------+
| rid | category | name    | fk_parent |
+-----+----------+---------+-----------+
| 1   | cat1     | one     | NULL      |
| 2   | cat1     | one.one | 1         |
| 3   | cat1     | one.two | 1         |
+-----+----------+---------+-----------+

 

< Duplicating the records >

 

INSERT INTO testing (category, name, fk_parent) (select category, name, fk_parent from testing where category='cat1') returning rid, category, name, fk_parent;

+-----+----------+---------+-----------+

| rid | category | name    | fk_parent |

+-----+----------+---------+-----------+

| 4   | cat1     | one     | NULL      |

| 5   | cat1     | one.one | 1         |

| 6   | cat1     | one.two | 1         |

+-----+----------+---------+-----------+

 

< What I'm looking for >

+--------------+-----+

| original_rid | rid |

+--------------+-----+

| 1            | 4   |

| 2            | 5   |

| 3            | 6   |

+--------------+-----+

 

< This doesn't work >

 

INSERT INTO testing (category, name, fk_parent) select category, name, fk_parent from testing as original where category='cat1' returning rid, category, name, fk_parent, original.rid;

 

 

Specifically, my goal is to be able to duplicate a subset of records and map any referenced foreign keys to the new ones from the copies. I could write a pl/pgsql function to loop through the records and build the mapping as I go, but I was thinking there might be a better way.  Any thoughts?

 

Thanks!

Michael

 

 

 

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> 

 

Two thoughts (syntax not validated):

 

INSERT INTO …. VALUES (non-id-cols, id)

SELECT [non-id-cols], nextval(‘sequence’) AS new_id FROM testing

RETURNING id, new_id

 

There is no reason to delay the assignment of the ID until the time of insert; by polling the sequence manually you get the same effect but at a time when you have not forgotten what the old value was.

 

If for some reason you have to let the ID be auto-generated you likely need to identify the “natural key” for the record and then:

 

WITH ins (

              INSERT …. RETURNING newid, (natural_key_cols) AS natrualkey

)

SELECT *

FROM ins

JOIN testing ON

ins.naturalkey = (testing.natural_key cols)

 

If there is no natural key then this method is ambiguous in the presence of multiple otherwise identical records.

 

David J