Aggregate function datatypes are not supported

[darkwanderer]

Aggregate function datatypes are not supported

[fenjas]

https://clickhouse.tech/docs/en/sql-reference/data-types/aggregatefunction/

[DarkWanderer]

Hi. AggregateFunction column does not make sense by itself - you can neither insert nor select data directly. It can only be handled with functions like ...State for insertion and ...Merge (e.g.: uniqState, uniqMerge) for selection. It's not possible to support it directly - you can't even get output for it from ClickHouse itself via JSON/TSV

To query AggregatedFunction-type column, you need to use a ...Merge function. In this case the correct way to select would be:
select <other fields>, argMaxMerge(device_group_name), argMaxMerge(transaction_country_alpha_2_code) from <table>

[DarkWanderer]

Solidified this in wiki for future reference