[SPARK-28645][SQL] ParseException is thrown when the window is redefined

[beliefer]

What changes were proposed in this pull request?

Currently in Spark one could redefine a window. For instance:

select count(*) OVER w FROM tenk1 WINDOW w AS (ORDER BY unique1), w AS (ORDER BY unique1);
The window w is defined two times. In PgSQL, on the other hand, a thrown will happen:

ERROR: window "w" is already defined

Why are the changes needed?

The current implement gives the following window definitions a higher priority. But it wasn't Spark's intention and users can't know from any document of Spark.
This PR fixes the bug.

Does this PR introduce any user-facing change?

Yes.
There is an example query output with/without this fix.

SELECT
    employee_name,
    salary,
    first_value(employee_name) OVER w highest_salary,
    nth_value(employee_name, 2) OVER w second_highest_salary
FROM
    basic_pays
WINDOW
    w AS (ORDER BY salary DESC ROWS BETWEEN UNBOUNDED PRECEDING AND 1 FOLLOWING),
    w AS (ORDER BY salary DESC ROWS BETWEEN UNBOUNDED PRECEDING AND 2 FOLLOWING)
ORDER BY salary DESC

The output before this fix:

Larry Bott	11798	Larry Bott	Gerard Bondur
Gerard Bondur	11472	Larry Bott	Gerard Bondur
Pamela Castillo	11303	Larry Bott	Gerard Bondur
Barry Jones	10586	Larry Bott	Gerard Bondur
George Vanauf	10563	Larry Bott	Gerard Bondur
Loui Bondur	10449	Larry Bott	Gerard Bondur
Mary Patterson	9998	Larry Bott	Gerard Bondur
Steve Patterson	9441	Larry Bott	Gerard Bondur
Julie Firrelli	9181	Larry Bott	Gerard Bondur
Jeff Firrelli	8992	Larry Bott	Gerard Bondur
William Patterson	8870	Larry Bott	Gerard Bondur
Diane Murphy	8435	Larry Bott	Gerard Bondur
Leslie Jennings	8113	Larry Bott	Gerard Bondur
Gerard Hernandez	6949	Larry Bott	Gerard Bondur
Foon Yue Tseng	6660	Larry Bott	Gerard Bondur
Anthony Bow	6627	Larry Bott	Gerard Bondur
Leslie Thompson	5186	Larry Bott	Gerard Bondur

The output after this fix:

struct<>
-- !query output
org.apache.spark.sql.catalyst.parser.ParseException

The definition of window 'w' is repetitive(line 8, pos 0)

How was this patch tested?

Jenkins test.

[SparkQA]

Test build #131824 has finished for PR 30512 at commit 43e8542.

• This patch fails Spark unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #131832 has finished for PR 30512 at commit 9f29766.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[beliefer]

cc @cloud-fan

[maropu]

The fix looks fine. In the PR description, could you add an example query output with/without this fix?

[beliefer]

The fix looks fine. In the PR description, could you add an example query output with/without this fix?

OK

[cloud-fan]

is the window spec name case insensitive?

[beliefer]

I checked the PgSQL and find the alias of window frame is case insensitive.

[cloud-fan]

thanks, merging to master!

[beliefer]

@cloud-fan @maropu Thanks for your work!