SQL Query

Table 1
PrimaryOrderID, AlternativeOrderID
123                             234
455                             238
233                             231
533                             345

Table2

OrderDate,     OrderID, Balance Owing
12/12/2000     231           $0.23
12/11/2000     238           $0.23
12/10/2000     232           $0.23
14/12/2000     455           $0.23
12/08/2000     234           $0.80
12/04/2000     123           $0.00
12/12/2000     345           $0.23
12/12/2000     533           $0.57

What I want is to

1. Find all records in Table2 where AlternativeOrderID from table1 has some balance owing matching orderid in table2.

2. Find all records in Table2 where AlternativeOrderID from table1 has some balance owing matching orderid in table2
In above result I want to see only those records where PrimaryOrderID exist in Table2

3. I want to update Table 2 by looking at Table 1 info such that any AlternativeOrderID balance owing in table 2 should add to PrimaryOrderID in table 2.
For example Alternative ID 345 has balance of $0.23 in Table 2 and and PrimaryOrderID of that is 533 with balance of 0.57
I want to update the table to that 0.23 cents adds to that 0.57 in table 2 so the result will be


OrderDate,     OrderID, Balance Owing
12/12/2000     345           $0.23
12/12/2000     533           $0.80

Can someone help please

Thanks,