對(duì)于下圖所示的S和SC關(guān)系,當(dāng)我們對(duì)其進(jìn)行左外連接時(shí),其結(jié)果集的屬性列數(shù)為 (1) ,元組個(gè)數(shù)為 (2) 。(1)A.6 B.7 C.8 D.9 (2)A.7 B.8 C.9 D.10