pgsql gives ExecutePlan error after empty UPDATE?

Hello! I am using PostgreSQL 7.0.2 on FreeBSD 3.4.

I am trying to update a table with the results of a
(possibly empty) selection:

zorro_4330=# create table foo(bar int4) \g
CREATE
zorro_4330=# update foo set bar = count(*) from foo \g
ERROR: ExecutePlan: (junk) `ctid' is NULL!

In this example, there are no rows in table "foo" to update.
Why is postgres returning this cryptic error instead of just UPDATE 0?

If I add a sample row, the same query works fine:

zorro_4330=# insert into foo values (1) \g
INSERT 50688 1
zorro_4330=# update foo set bar = count(*) from foo \g
UPDATE 1

If I change my query to update no rows, I get the error again:

zorro_4330=# update foo set bar = count(*) from foo where bar < 0 \g
ERROR: ExecutePlan: (junk) `ctid' is NULL!

Postgres seems to be reporting an error because the update matched no rows,
but this a perfectly legitimate database operation. I have not
been able to find any documentation on "ExecutePlan" or why it
thinks there is a problem.

Please let me know if you have any suggestions or workarounds for this problem,
or if there is somewhere more appropriate to discuss this. Thanks!

David

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David C Mudie DigitalDeck Inc mudie(at)digitaldeck(dot)com
San Mateo CA 94402 http://www.digitaldeck.com