Using generate_series to create a unique ID in a query?

Hello,

I am trying to create a view that will contain a generated sequence
(unique ID), and am running into problems doing so.

For some context, I am trying to create a report that provides a list of
client charges and payments and a "running balance" after each
transaction. Because  we often have multiple charges and/or payments on
the same day, we can't use the transaction date to calculate this
balance.  Instead, I want to calculate our running balance by assigning
a transaction ID to each transaction a d then having the query sum up
transaction amounts for all transactions with an equal or lower ID.

I can use generate_series to produce a set of IDs, but can't get it to
join properly to the rest of my query.  For example, if I had 10 rows in
my query, I would get a series of 1 to 10, but would then get 100 rows
(10x10) in my result.  Ultimately the results of this query are going to
be used as a view, so I'd like to avoid creating a temp table, sequence,
etc. Does anyone know how to use generate_series in this manner, or know
of some other way I can go about this?  Thanks in advance!

To recap with an example, the query below works fine, but how do I add a
series to it?

SELECT * FROM (

SELECT
          client_id,
          effective_date AS transaction_date,
          amount AS charge_amount,
          0 AS payment_amount
   FROM    charge
   UNION
   SELECT
           client_id,
           payment_date AS transaction_date,
           0 as charge_amount,
           amount AS payment_amount
   FROM payment

) AS tmp
ORDER BY
   transaction_date,
   charge_amount<>0 /* order charges before payments */

Thanks,
Sarah Dougherty