PostgreSQL Bugs - Re: Double sequence increase on single insert with RULE on

Author

Re: Double sequence increase on single insert with RULE on

Sarunas Krisciukaitis

2005-11-16, 7:25 am

I understand that RULES are like macros.
Strangest thing here is that INSERT to test1 will touch only one
sequence: test1_id_seq.
And it increments test1_id_seq twice during insert with RULE.
Then all sequence procedures like lastval() and currval() will return
number (as stated in report),
which is biger than actualy one inserted into the database.
When after insert:
BEGIN; INSERT INTO test1(some_text) VALUES ('test1'); SELECT lastval()
as id; END;
you make a select on test1 and test_log1 tables you see such a view:
testdb=# select * from test1;
id | some_text
----+-----------
2 | test1
(1 row)
testdb=# select * from test_log1;
qid | when_happened
-----+----------------------------
3 | 2005-11-16 10:27:33.100913
(1 row)

Sarunas

Tomas Zerolo wrote:

>On Tue, Nov 15, 2005 at 10:51:10PM -0700, Michael Fuhr wrote:
>
>
>
>[...]
>
>Oops, I didn't see that. Your eyes are sharper than mine ;-)
>
>thanks
>-- tomas
>
>

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Sarunas Krisciukaitis

2005-11-18, 9:24 am

Ok :) Then I found the solution in this partical case:
CREATE RULE test1_on_insert AS ON INSERT TO test1 DO INSERT INTO
test_log1 (qid) VALUES ( (SELECT lastval()) );
With this rule all inserts are working as expected :)

Thank you for you advise :)

Sarunas

Michael Fuhr wrote:

>On Wed, Nov 16, 2005 at 10:31:10AM +0200, Sarunas Krisciukaitis wrote:
>
>
>
>Yes, that's a well-known effect of rewriting a query that includes
>a call to nextval(). NEW.id in the rule doesn't refer to the value
>that's inserted, but rather to the expression that's evaluated to
>get that value. Since you didn't provide a value for id it gets
>the default: nextval('test1_id_se
q'). That expression is used in
>both inserts, so the sequence gets incremented twice. See the
>archives for numerous past discussions of this behavior.
>
>
>

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