sql problem

[Pikachu]

Was spricht denn gegen zwei SELECTs, verbunden durch ein UNION?

SELECT F.RECHNR, F.ANSKUNDE, F.KUNDENNR,                
SUBSTR(A.FELD1,  1, 4) AS NAME,                         
SUBSTR(A.FELD1,  5, 6) AS STRASSE,                      
SUBSTR(A.FELD1, 11, 3) AS ORT                           
FROM FILE F INNER JOIN FILEA A ON F.KUNDENNR=A.KUNDENNR
WHERE ANSKUNDE  ='X'                                    
UNION                                                   
SELECT F.RECHNR, F.ANSKUNDE, F.KUNDENNR,                
SUBSTR(B.FELD1,  1, 4) AS NAME,                         
SUBSTR(B.FELD1,  5, 6) AS STRASSE,                      
SUBSTR(B.FELD1, 11, 3) AS ORT                           
FROM FILE F INNER JOIN FILEB B ON F.KUNDENNR=B.KUNDENNR
WHERE ANSKUNDE <>'X'