单项选择题
A.select book_name，book_price from book ；B.select *from book；C.select book from book_name，book_price ；D.select *from book book_name，book_price；
A.select *from xs group by 学号desc；B.select *from xs order by 学号ascC.select *from xs order by 学号desc；D.select *from xs 学号order by；
A.UNIONB.DISTINCTC.ALLD.TOP