MariaDB [test]> create table cs1(v8 varchar(8), t text ) engine=columnstore;

Query OK, 0 rows affected (0.92 sec)

MariaDB [test]> insert into cs1 values ('some','other'),('some2','other2');

Query OK, 2 rows affected (0.43 sec)

Records: 2  Duplicates: 0  Warnings: 0

MariaDB [test]> create table i1 (v8 varchar(8), t text);

Query OK, 0 rows affected (0.53 sec)

MariaDB [test]> insert into i1 select * from cs1;

sQuery OK, 2 rows affected (0.58 sec)

Records: 2  Duplicates: 0  Warnings: 0

MariaDB [test]> select * from i1;

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

| v8    | t      |

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

| some  | other  |

| some2 | other2 |

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

2 rows in set (0.00 sec)

MariaDB [test]> select * from cs1;

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

| v8    | t      |

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

| some  | other  |

| some2 | other2 |

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

2 rows in set (0.01 sec)

MariaDB [test]> update cs1 set v8 = 'NULL' where v8 = 'some';

Query OK, 1 row affected (0.14 sec)

Rows matched: 0  Changed: 0  Warnings: 0

MariaDB [test]> select * from cs1 where v8 is null;

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

| v8   | t     |

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

| NULL | other |

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

1 row in set (0.02 sec)

MariaDB [test]> update i1 set v8 = 'NULL' where v8 = 'some';

Query OK, 1 row affected (0.15 sec)

Rows matched: 1  Changed: 1  Warnings: 0

MariaDB [test]> select * from i1 where v8 is null;

Empty set (0.00 sec)

MariaDB [test]> update i1 set t = 'NULL' where v8 = 'some2';

Query OK, 1 row affected (0.23 sec)

Rows matched: 1  Changed: 1  Warnings: 0

MariaDB [test]> select * from i1 where t is null;

Empty set (0.00 sec)

MariaDB [test]> update cs1 set t = 'NULL' where v8 = 'some2';

Query OK, 1 row affected (0.15 sec)

Rows matched: 0  Changed: 0  Warnings: 0

MariaDB [test]> select * from cs1 where t is null;

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

| v8    | t    |

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

| some2 | NULL |

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

1 row in set (0.02 sec)