SELECT
	X.ID, A.TotA, B.TotB
FROM
	(SELECT
		SUM(FieldA) as TotA
	FROM
		TableA
		INNER JOIN TableA2 ON TableA.ID = TableA2.pID
	WHERE
		TableA2.XID = X.ID
	) A,
	(SELECT
		SUM(FieldB) as TotB
	FROM
		TableB
		INNER JOIN TableB2 ON TableB.ID = TableB2.pID
	WHERE
		TableB2.XID = X.ID
	) B
WHERE
	X.pID = @SomePID