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Columnstore engine does not store empty strings in varchar or text columns, it replaces them with null.
MariaDB [wh]> show session status like 'Columnstore_version';
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Variable_name Value
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Columnstore_version 6.1.1
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MariaDB [wh]> truncate table p;
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MariaDB [wh]> show create table p;
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Table Create Table
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p CREATE TABLE `p` (\n `col1` varchar(100) DEFAULT NULL\n) ENGINE=Columnstore DEFAULT CHARSET=utf8mb3
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MariaDB [wh]> insert into p values (null);
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MariaDB [wh]> insert into p values ('');
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MariaDB [wh]> select * from p;
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col1
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NULL
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NULL
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MariaDB [wh]>
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If the column is defined as varchar NOT NULL there is a conflict, which throws an error.
MariaDB [wh]> CREATE TABLE `q`(`col1` varchar(100) NOT NULL DEFAULT '')ENGINE=Columnstore DEFAULT CHARSET=utf8mb3;
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MariaDB [wh]> insert into q values('');
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ERROR 1815 (HY000): Internal error: CAL0001: Insert Failed: IDB-4015: Column 'col1' cannot be null.
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MariaDB [wh]>
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MariaDB [wh]> CREATE TABLE `u`(`col1` varchar(100) NOT NULL DEFAULT '')ENGINE=innodb DEFAULT CHARSET=utf8mb3;
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MariaDB [wh]> insert into u values ('');
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MariaDB [wh]> insert into u values (null);
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ERROR 1048 (23000): Column 'col1' cannot be null
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MariaDB [wh]>
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