Re: Avoiding RI failure with INSERT ... SELECT FROM

On 7/12/06, Mark Stosberg <mark(at)summersault(dot)com> wrote:
>
>
> Hello! I got an unexpected SQL failure last night, and want to see how
> to prevent it in the future. This is with 8.1.3.
>
> I have a couple of insert statements that run in a transaction block,
> initializing rows that will be used the next day:
>
> INSERT into item_hit_log
> SELECT item_id, CURRENT_DATE + CAST('1 day' AS interval), 0
> FROM items where item_state = 'available';
>
> INSERT into item_view_log
> SELECT item_id, CURRENT_DATE + CAST('1 day' AS interval), 0
> FROM items where item_state = 'available';

I would recommend you list your values in your insert statements:

INSERT into item_hit_log (
item_id_fk, ....
)
SELECT ....

That makes it less prone to problems in the future (like if the column
orders change) and makes it easier for others to understand and help you
with.

The "items" table has a few hundred thousand rows in it, so this takes a
> bit a run.
>
> The error we got last night was:
>
> ERROR: insert or update on table "item_hit_log" violates foreign key
> constraint "item_id_fk"
> DETAIL: Key (item_id)=(451226) is not present in table "items".
>
> Re-running the transaction block a few minutes later worked.
>
> What's an alternate design that avoids this possible error?

Does the items table allow deletes? If so, your insert may be attempting to
do an insert for an item_id that was deleted after the select and before the
insert. Don't know if PostgreSQL will prevent that with table locking or
not.

==================================================================
Aaron Bono
Aranya Software Technologies, Inc.
http://www.aranya.com
==================================================================