Just building on what you already have...
SELECT Group, SUM(Received), SUM(Paid)
FROM (
SELECT a.ReceiverGroup AS Group, SUM(a.Value) as Received, 0 as Paid
FROM Test a
Group by a.ReceiverGroup
UNION ALL
SELECT b.PayerGroup as Group, 0 as Received, SUM(b.Value) as Paid
FROM Test b
Group by b.PayerGroup
) AS c
GROUP BY Group
Assuming SUM is the correct aggregation for Received and Paid
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... Then again, I could be totally wrong! Check the answer.
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