Incremental Models with Subqueries best practices

Help
1

I haven’t found much information about how people deal with incremental models in a query with many subqueries. Example:

{{ config( materialized='incremental') }}

with a as (
select * from table_a
       {% if is_incremental() %}
        where a_insert_date>= (select max(a_insert_date) from {{ this }} )
        {% endif %}
),
b as (select * from table_b
        {% if is_incremental() %}
        where a_insert_date>= (select max(a_insert_date) from {{ this }} )
        {% endif %}
)
select *
from a
left join b on key_a = key_b

I would like to use the unique_key=‘my_unique_key’ so if the key is updated the new data is replaced.
But because now I have multiple subqueries, there are multiple unique keys per query.

My approach would be to add another condition per subquery:

and my_unique_key_a  NOT IN (SELECT my_unique_key_a  FROM table_a )

But there have to be smarter ways. What is your approach ?

Thanks in advance!