[defcon1_es]

Hola. Prueba con la función COALESCE.

Código SQL [-]
SELECT recibos.ID_CLAVE AS ID_RECIBO,        
recibos.MONTH AS MONTH,       
COALESCE( (SELECT recibo_ingresos.CANTIDAD FROM recibo_ingresos 
              WHERE recibo_ingresos.ID_RECIBO = recibos.ID_CLAVE), 0) AS ALQUILER,       
COALESCE( (SELECT SUM(recibo_ingresos.TOTAL) FROM recibo_ingresos 
              WHERE recibo_ingresos.ID_RECIBO = recibos.ID_CLAVE), 0) AS TOTAL_INGRESOS,       
COALESCE( (SELECT SUM(CASE WHEN recibo_gastos.TOTAL ISNULL THEN 0 ELSE recibo_gastos.TOTAL END)
              FROM recibo_gastos WHERE recibo_gastos.ID_RECIBO = recibos.ID_CLAVE), 0) AS TOTAL_GASTOS   
FROM recibos  
WHERE recibos.ID_CONTRATO = "0000000024"    AND 
          recibos.YEAR = "2009"