Postgresql select until certain total amount is reached

Question

I was wondering if I could get any help with the following problem.

I have a table of transactions (simplified below) and I only want to select transactions until my

Answer 1

select id, 
       date, 
       amount, 
       running_total
from (
    select id,
           date,
           amount,
           sum(amount) over (order by date asc) as running_total
    from transactions
) t
where running_total <= 6

Answer 2

select T1.*
from Transactions as T1
where 6 - (select sum(T2.amount) 
               from Transactions as T2 where  T2.id <= T1.id
          ) >= 0
order by id asc

This query works on SQL Server if Postgres supports subqueries like SQL Server does it can help you

Answer 3

Although it may not be the most efficent way (as you're still, in essence, selecting everything first), I'd look at using a running total.

Something like:

SELECT
  *
FROM
  (
  SELECT
    id
    , date
    , amount
    , (SELECT SUM(amount) FROM Transactions WHERE id <= t.id) AS RunningTotal
  FROM
    Transactions t
) t1
WHERE
  t1.RunningTotal < 6