You can do something like this. This query can be created and run on the client:
``` const SAMPLE_JOIN_QUERY = gql` query ($main_data_id: String!) { mainData( main_data_id: $main_data_id) { id main_data_field_1 main_data_field_2 main_data_field_3 related_data{ related_data_field_1 related_data_field_2 related_data_field_3 } } } `; ```