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@digitaldeck.com
San Mateo CA 94402 http://www.digitaldeck.com
David C Mudie <mudie@digitaldeck.com> writes:
zorro_4330=# update foo set bar = count(*) from foo \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.
Actually, it's flat-out illegal according to SQL92: thou shalt not
use an aggregate in UPDATE, quoth the standard. Try it with the
count() in a sub-select, which is legal SQL:
update foo set bar = (select count(*) from foo);
There is a thread going on in pghackers right now about whether it
makes sense to allow aggregates outside sub-selects in UPDATE, and
if so what it should mean exactly.
regards, tom lane