DROP DATABASE IF EXISTS mcol641_union_db;

CREATE DATABASE mcol641_union_db;
USE mcol641_union_db;

SET SQL_MODE='ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION';

CREATE TABLE cs1 (d1 DECIMAL(38), d2 DECIMAL(38,10), d3 DECIMAL(38,38)) ENGINE=columnstore;
CREATE TABLE cs2 (d1 DECIMAL(38) UNSIGNED, d2 DECIMAL(38,10) UNSIGNED, d3 DECIMAL(38,38) UNSIGNED) ENGINE=columnstore;

INSERT INTO cs1 VALUES (125, 1.25, 0.125);
INSERT INTO cs1 VALUES (-125, -1.25, -0.125);
INSERT INTO cs1 values (99999999999999999999999999999999999998, 9999999999999999999999999999.9999999998, 0.99999999999999999999999999999999999998);
INSERT INTO cs1 values (99999999999999999999999999999999999999, 9999999999999999999999999999.9999999999, 0.99999999999999999999999999999999999999);
INSERT INTO cs1 values (-99999999999999999999999999999999999998, -9999999999999999999999999999.9999999998, -0.99999999999999999999999999999999999998);
INSERT INTO cs1 values (-99999999999999999999999999999999999999, -9999999999999999999999999999.9999999999, -0.99999999999999999999999999999999999999);

SELECT d1, d1, d2 FROM cs1 UNION SELECT d2, d3, d3 FROM cs1;

SHOULD GIVE

d1 d1 d2
125.0000000000 125.00000000000000000000000000000000000000 1.25000000000000000000000000000000000000
-125.0000000000 -125.00000000000000000000000000000000000000 -1.25000000000000000000000000000000000000
99999999999999999999999999999999999998.0000000000 999999999999999999999999999.99999999999999999999999999999999999999 999999999999999999999999999.99999999999999999999999999999999999999
99999999999999999999999999999999999999.0000000000 999999999999999999999999999.99999999999999999999999999999999999999 999999999999999999999999999.99999999999999999999999999999999999999
-99999999999999999999999999999999999998.0000000000 -999999999999999999999999999.99999999999999999999999999999999999999 -999999999999999999999999999.99999999999999999999999999999999999999
-99999999999999999999999999999999999999.0000000000 -999999999999999999999999999.99999999999999999999999999999999999999 -999999999999999999999999999.99999999999999999999999999999999999999
1.2500000000 0.12500000000000000000000000000000000000 0.12500000000000000000000000000000000000
-1.2500000000 -0.12500000000000000000000000000000000000 -0.12500000000000000000000000000000000000
9999999999999999999999999999.9999999998 0.99999999999999999999999999999999999998 0.99999999999999999999999999999999999998
9999999999999999999999999999.9999999999 0.99999999999999999999999999999999999999 0.99999999999999999999999999999999999999
-9999999999999999999999999999.9999999998 -0.99999999999999999999999999999999999998 -0.99999999999999999999999999999999999998
-9999999999999999999999999999.9999999999 -0.99999999999999999999999999999999999999 -0.99999999999999999999999999999999999999

BUT GIVES (~random incorrect values in columns)

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RUN WITHOUT COLUMNSTORE GIVES CORRECT RESULT:

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Single selects without union:
SELECT d1, d1, d2 FROM cs1;
SELECT d2, d3, d3 FROM cs1;
work fine.