Different SQL, same principle. Only insert if the clause in where not exists fails
INSERT INTO FX_USDJPY
(PriceDate,
PriceOpen,
PriceLow,
PriceHigh,
PriceClose,
TradingVolume,
TimeFrame)
SELECT '2014-12-26 22:00',
120.369000000000,
118.864000000000,
120.742000000000,
120.494000000000,
86513,
'W'
WHERE NOT EXISTS
(SELECT 1
FROM FX_USDJPY
WHERE PriceDate = '2014-12-26 22:00'
AND TimeFrame = 'W')