ROUND(d1,38)/TRUNCATE(d1,38) where d1 is DECIMAL(38)/DECIMAL(38,10) gives wrong results.

MariaDB [test]> drop table if exists cs1;

Query OK, 0 rows affected (0.293 sec)

MariaDB [test]> create table cs1(d1 decimal(38,10))engine=columnstore;

Query OK, 0 rows affected (0.258 sec)

MariaDB [test]> insert into cs1 values (9999999999999999999999999999.9999999999), (1234567890123456789012345678.9012345678);

Query OK, 2 rows affected (0.293 sec)

Records: 2  Duplicates: 0  Warnings: 0

MariaDB [test]> select round(d1, 38), truncate(d1, 38) from cs1;

+--------------------------------------------------------------------+--------------------------------------------------------------------+

| round(d1, 38)                                                      | truncate(d1, 38)                                                   |

+--------------------------------------------------------------------+--------------------------------------------------------------------+

| 999999999999999999999999999.99999999999999999999999999999999999999 | 999999999999999999999999999.99999999999999999999999999999999999999 |

| 999999999999999999999999999.99999999999999999999999999999999999999 | 999999999999999999999999999.99999999999999999999999999999999999999 |

+--------------------------------------------------------------------+--------------------------------------------------------------------+

2 rows in set (0.093 sec)

The expected results are:

MariaDB [test]> select round(d1, 38), truncate(d1, 38) from cs1;

+---------------------------------------------------------------------+---------------------------------------------------------------------+

| round(d1, 38)                                                       | truncate(d1, 38)                                                    |

+---------------------------------------------------------------------+---------------------------------------------------------------------+

| 9999999999999999999999999999.99999999990000000000000000000000000000 | 9999999999999999999999999999.99999999990000000000000000000000000000 |

| 1234567890123456789012345678.90123456780000000000000000000000000000 | 1234567890123456789012345678.90123456780000000000000000000000000000 |

+---------------------------------------------------------------------+---------------------------------------------------------------------+

2 rows in set (0.001 sec)

MariaDB [test]> drop table if exists cs1;

Query OK, 0 rows affected (0.235 sec)

MariaDB [test]> CREATE TABLE cs1 (d1 DECIMAL(38)) ENGINE=columnstore;

Query OK, 0 rows affected (0.166 sec)

MariaDB [test]> INSERT INTO cs1 VALUES (9999999999999999999999999999999999999);

Query OK, 1 row affected (0.171 sec)

MariaDB [test]> select round(d1, 38), truncate(d1, 38) from cs1;

+--------------------------------------------------------------------+--------------------------------------------------------------------+

| round(d1, 38)                                                      | truncate(d1, 38)                                                   |

+--------------------------------------------------------------------+--------------------------------------------------------------------+

| 999999999999999999999999999.99999999999999999999999999999999999999 | 999999999999999999999999999.99999999999999999999999999999999999999 |

+--------------------------------------------------------------------+--------------------------------------------------------------------+

1 row in set (0.114 sec)

MariaDB [test]> select round(d1, 38), truncate(d1, 38) from cs1;

+----------------------------------------------------------------------------+----------------------------------------------------------------------------+

| round(d1, 38)                                                              | truncate(d1, 38)                                                           |

+----------------------------------------------------------------------------+----------------------------------------------------------------------------+

| 9999999999999999999999999999999999999.000000000000000000000000000000000000 | 9999999999999999999999999999999999999.000000000000000000000000000000000000 |

+----------------------------------------------------------------------------+----------------------------------------------------------------------------+

1 row in set (0.001 sec)