Just to add:

The basic pattern here for a table A and a query Q that involves a join to A is to turn the query into a derived query and join that with A:

UPDATE A
SET A.x = DT.y
FROM A INNER JOIN (Q) DT ON <join-condition>;

I find it all too easy to forget just how much can be done with derived queries! Had an embarrassing example recently where rewriting a loop as a derived summary query reduced execution time by 98%.

I assume that you want to update some column let say column name is iscustomernegative in table A_Sales_Ledger.

For example: update A_Sales_Ledger set iscustomernegative = 'YES';

Then I would write my statement as follows:

update A_Sales_Ledger set iscustomernegative = 'YES' where Customer_ID in

(select Customer_ID from (

SELECT SUM(Debit) as 'Debit_Total', SUM(Credit) as 'Credit_Total', Customer_ID, Sum(Debit)- Sum(Credit) as 'Balance' FROM A_Sales_Ledger GROUP BY Customer_ID HAVING Balance <= 0 ORDER BY Balance

) TRANS_TABLE)