SELECT
SUM( a.amountfigure ) AS 'Dollars'
, 'Buying' AS 'Transact'
FROM forex_tbl a
WHERE a.currency = 'USD' AND a.transactiontype = 'Buying'

UNION ALL

SELECT
SUM( b.amountfigure ) AS 'Dollars'
, 'Selling' AS 'Transact'
FROM forex_tbl b
WHERE b.currency = 'USD' AND b.transactiontype = 'Selling';

SELECT
(SELECT
SUM( a.amountfigure ) AS 'Dollars'
FROM forex_tbl a
WHERE a.currency = 'USD' AND a.transactiontype = 'Buying') AS 'Buying'

,(SELECT
SUM( b.amountfigure ) AS 'Dollars'
FROM forex_tbl b
WHERE b.currency = 'USD' AND b.transactiontype = 'Selling') AS 'Selling';

SELECT Sum(CASE WHEN transactiontype = 'Buying'  THEN amountfigure END) As [Buying]
     , Sum(CASE WHEN transactiontype = 'Selling' THEN amountfigure END) As [Selling]
FROM   forex_tbl
WHERE  currency = 'USD'

SELECT Sum(CASE WHEN transactiontype = 'Buying'  THEN amountfigure END)
     - Sum(CASE WHEN transactiontype = 'Selling' THEN amountfigure END) As [Dollars]
FROM   forex_tbl
WHERE  currency = 'USD'