Stephan Szabo wrote:
On Tue, 2 Oct 2007, Jeff Frost wrote:
I expected these numbers to be in sync, but was suprised to see that the
sequence skips a values after every generate series.
CREATE TABLE jefftest ( id serial, num int );
INSERT INTO jefftest (num) values (generate_series(1,10));
INSERT INTO jefftest (num) values (generate_series(11,20));
INSERT INTO jefftest (num) values (generate_series(21,30));
It seems to do what you'd expect if you do
INSERT INTO jefftest(num) select a from generate_series(1,10) as foo(a);
INSERT INTO jefftest(num) select a from generate_series(11,20) as foo(a);
INSERT INTO jefftest(num) select a from generate_series(21,30) as foo(a);
I tried a function that raises a notice and called it as
select f1(1), generate_series(1,10);
and got 11 notices so it looks like there's some kind of phantom involved.
That's interesting - might need an answer from the core hackers.
I am posting this to pgsql-hackers to get their comments and feedback.
I wouldn't count it as a bug but it could be regarded as undesirable
My guess is that what appears to happen is that the sequence is created
by incrementing as part of the insert steps and the test to check the
end of the sequence is -
if last_inserted_number > end_sequence_number
This would explain the skip in sequence numbers.
My thoughts are that -
if last_inserted_number < end_sequence_number
would be a better way to approach this. Of course you would also need to
check that the (last_insert + step_size) isn't greater than the
end_sequence_number when the step_size is given.
I haven't looked at the code so I don't know if that fits easily into
the flow of things.
The as foo(a) test would fit this as the sequence is generated into the
equivalent of a temporary table the same as a subselect, then used as
insert data. The rollback would be applied during the temporary table
generation so won't show when the data is copied across to fulfill the
Maybe the planner or the generate series function could use a temporary
table to give the same results as select from generate_series()
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