How to merge different derived tables

[Rub_moy]

Dear experts,

I need to merge 2 different explores but I don't want to do it in the visualisation process but with code.

I've created 2 different derived tables with the same amount of fields and names. Example:

derived_table: {
explore_source: bookings {
column: pvp_amount { field: service.pvp_amount }
column: start_date { field: service.start_date }
column: channel{ field: properties.channel}
}
}
derived_table: {
explore_source: sales{
column: pvp_amount { field: sales.pvp_amount }
column: start_date { field: sales.start_date }
column: channel{ field: properties.channel}
}
}

I though about joining the two tables with a full outer join, but none of them has a primary key. What should I use in sql_on ? Should I concatenate start_date and channel as a Primary fot both tables and use them in sql_on?

Is there any other way to union explores?

Thanks in advance

UPDATE: I've tried full outer join but it just keeps fields from both tables