Type convertion problems columnstore

Hello,

the SELECT at the end of the example below provides wrong NULL values as result for
the columns s2, s3 and s4.

Best regards

DROP TABLE IF EXISTS fact;
CREATE TABLE fact (
atc INT(11),
v1 INT(11)
)
ENGINE=Columnstore;

INSERT INTO fact VALUES
(1,11),
(2,22);

CREATE OR REPLACE VIEW v_fact_primary AS
SELECT
atc,
v1
FROM fact;

CREATE OR REPLACE VIEW v_fact_secondary AS
SELECT
atc,
v1,
CAST(0 AS UNSIGNED) AS v2 – without CAST one gets "the storage engine ... doesn't support Unknown REF item
FROM v_fact_primary;

SELECT
atc,
SUM(v1) AS sum1,
SUM(v2) AS sum2,
CAST(SUM(v1) AS CHAR(100)) AS s1,

CAST(SUM(v2) AS CHAR(100)) AS s2, – not working
CONVERT(SUM(v2),CHAR) AS s3, – not working
'' + SUM(v2) AS s4 – not working
FROM
v_fact_secondary
GROUP BY atc;