SQL Server 2019

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create table orders (
  orderId integer, 
  customerId integer, 
  orderedDate date
  );
insert into orders values 
(1, 1000, '2024-02-27'), 
(2, 2000, '2024-02-28'), 
(3, 3000, '2024-02-28'), 
(4, 1000, '2024-02-29'), 
(5, 4000, '2024-02-29'); 
  
5 rows affected

--Using CTE, but calls table twice (less efficient)
with first_orders as (
  select customerId, min(orderedDate) as min_dt
  from orders
  group by customerId
  )
select o.*
  from orders o
  join first_orders f
    on o.customerId = f.customerId
where f.min_dt >= '2024-02-28';


orderId
customerId
orderedDate


2
2000
2024-02-28

3
3000
2024-02-28

5
4000
2024-02-29


--Using windows function, calls table just once
select 
 orderId, customerId, orderedDate
from (
select *, 
 min(orderedDate) over (partition by customerId) as min_dt
from orders
  )z
where min_dt >= '2024-02-28'
order by customerId;


orderId
customerId
orderedDate


2
2000
2024-02-28

3
3000
2024-02-28

5
4000
2024-02-29