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Batch mode window aggregate arithmetic overflow bug

The following query performs a windowed SUM over a columnstore table with 1500 total rows, each of which has the value 0 or 1, and it overflows the INT data type. This appears to be a bug in the batch mode window aggregate operator.

SELECT a, p, s, v, m, n,
SUM(CASE WHEN n IS NULL THEN 0 ELSE 1 END)
OVER (PARTITION BY s, v, a ORDER BY p) AS lastNonNullPartition
FROM (
SELECT a, p, s, v, m, n,
RANK() OVER (PARTITION BY v, s, a, p ORDER BY m) AS rank
FROM #t /* A columnstore table with 1,500 rows */
) x
WHERE x.rank = 1
--Msg 8115, Level 16, State 2, Line 1521
--Arithmetic overflow error converting expression to data type int.

If any of the following modifications are made, the error does not occur:

* Use trace flag 8649 to prefer a parallel plan regardless of the cost threshold for parallelism
* Use trace flag 9453 to disable batch mode
* Use the COUNT aggregation function instead of the SUM function
* Remove the WHERE x.rank = 1 predicate

See https://dba.stackexchange.com/questions/218634 for many more details and comments.

See https://gist.github.com/pattertall/2875082fe045c90b253c24a954d4f6fc (or the attached file) for a full reproduction script. This bug reproduces in SQL Server 2016, 2017, and 2019 CTP.

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