Foros Club Delphi - Restar registros de diferentes tablas !!!

Hola Buenas Tardes tengo una Sql a la que necesito restarle otra, pero no se cómo.

Código SQL [-] SELECT SUM(IMP) 
FROM( select M.IMP FROM expemov M INNER JOIN EXPEDIENTES E ON E.ID = M.IDEXP         
WHERE M.IDEXP between   :EXP1 AND :EXP2            AND DH = 'D'           AND SDP = 'P' 
union all   
select  -m.IMP FROM expemov m INNER JOIN EXPEDIENTES E ON E.ID = M.IDEXP   
WHERE M.IDEXP  between  :EXP1 AND :EXP2            AND DH = 'H'           AND SDP = 'P') AS T

Esta es la primera select,.....y quiero restarle a la primera ésta otra

Código SQL [-]SELECT SUM(IMP) FROM EXPEPRV          WHERE IDEXP  between  :EXP1 AND :EXP2

y que me muestre los resultados que no sean 0.

Gracias por todo, tengo un buen cacao con esto..xD

Código SQL [-]

 SELECT SUM(IMP) 
FROM( select M.IMP FROM expemov M INNER JOIN EXPEDIENTES E ON E.ID = M.IDEXP         
WHERE M.IDEXP between   :EXP1 AND :EXP2            AND DH = 'D'           AND SDP = 'P' 
HAVING SUM(IMP) <> 0
union all   
select  -m.IMP FROM expemov m INNER JOIN EXPEDIENTES E ON E.ID = M.IDEXP   
WHERE M.IDEXP  between  :EXP1 AND :EXP2            AND DH = 'H'           AND SDP = 'P') AS T
AND M.IMP <> 0

MINUS

SELECT SUM(IMP) FROM EXPEPRV          WHERE IDEXP  between  :EXP1 AND :EXP2
HAVING SUM(IMP) <> 0