How do query optimizers affect window functions

Hi, Postgresql,

I want to understand how the query optimizers affect the output of the
window functions.

For example, set "cpu_tuple_cost = 50" in postgresql.conf and start the
server, I apply the regress test (make installcheck). The test of window
function fails.

Checking the diff and I found the output of the window functions are
different. For example,

For the following query:

SELECT sum(unique1) over (rows between current row and unbounded
following), unique1, four FROM tenk1 WHERE unique1 < 10;

The expected results are:

sum | unique1 | four
-----+---------+------
45 | 4 | 0
41 | 2 | 2
39 | 1 | 1
38 | 6 | 2
32 | 9 | 1
23 | 8 | 0
15 | 5 | 1
10 | 3 | 3
7 | 7 | 3
0 | 0 | 0

But the real results are:

sum | unique1 | four
-----+---------+------
45 | 0 | 0
45 | 1 | 1
44 | 2 | 2
42 | 3 | 3
39 | 4 | 0
35 | 5 | 1
30 | 6 | 2
24 | 7 | 3
17 | 8 | 0
9 | 9 | 1

There're altogether 6 queries in window test that outputs different query
results.

I don't understand why the results are different. Intuitively, the queries
show return the same results no matter what plan the optimizer choose.

I suspected the previous queries had some side effect on the latter one
(e.g., change the current row), so I removed all the previous queries
before this query in window.sql. But the result did not change.

Could anyone explain this behavior? Or point out how to investigate?

Thanks a lot!
Tianyin