Aggregate before and after a date column - sql

Question

I have two tables: db.transactions and db.salesman, which I would like to combine in order to create an output that has aggregated sales before each salesman's hire date and after each salesman's hire date.
select * from db.transactions
index sales_rep sales trx_date
1 Tom 200 9/18/2020
2 Jerry 435 6/21/2020
3 Patrick 1400 4/30/2020
4 Tom 560 5/24/2020
5 Francis 240 1/2/2021
select * from db.salesman
index sales_rep hire_date
1 Tom 8/19/2020
2 Jerry 1/28/2020
3 Patrick 4/6/2020
4 Francis 9/4/2020
I would like to aggregate sales from db.transactions before and after each sales rep's hire date.
Expected output:
index sales_rep hire_date agg_sales_before_hire_date agg_sales_after_hire_date
1 Tom 8/19/2020 1200 5000
2 Jerry 1/28/2020 500 900
3 Patrick 4/6/2020 5000 300
4 Francis 9/4/2020 2900 1500
For a single sales rep, to calculate the agg_sales_before_hire_date is likely:
select tx.sales_rep, tx.sum(sales)
from db.transactions tx
inner join db.salesman sm on sm.sales_rep = tx.sales_rep
where hire_date < '8/19/2020' and sales_rep = 'Tom'
group by tx.sales_rep
PostGRESQL. I am also open to the idea of doing it into Tableau or Python.

Answer 1

Using CROSS JOIN LATERAL
select
sa.sales_rep, sa.hire_date,
l.agg_sales_before_hire_date,
l.agg_sales_after_hire_date
from salesman sa
cross join lateral
(
select
sum(tx.sales) filter (where tx.trx_date < sa.hire_date) agg_sales_before_hire_date,
sum(tx.sales) filter (where tx.trx_date >= sa.hire_date) agg_sales_after_hire_date
from transactions tx
where tx.sales_rep = sa.sales_rep
) l;

Answer 2

Use conditional aggregation:
select tx.sales_rep,
sum(case when tx.txn_date < sm.hire_date then sales else 0 end) as before_sales,
sum(case when tx.txn_date >= sm.hire_date then sales else 0 end) as after_sales
from db.transactions tx inner join
db.salesman sm
on sm.sales_rep = tx.sales_rep
group by tx.sales_rep;
EDIT:
In Postgres, you would use filter for the logic:
select tx.sales_rep,
sum(sales) filter (where tx.txn_date < sm.hire_date) as before_sales,
sum(sales) filter (where tx.txn_date >= sm.hire_date then sales) as after_sales