From: pgsql-general-ow...@postgresql.org
[mailto:pgsql-general-ow...@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
