数据库问题2 请高人解答 谢谢

create table C
(
CNo CHAR(10),
Cn FLOAT,
PRIMARY KEY(CNo),
FOREIGN KEY (CNo) REFERENCES T(TNo)
);

select T.TNo,T.TN,C.Cn
from T,C
where T.TNo=C.CNo

create table C(
CNo varchar(10) primary key foreign key(CNo) References T(TNo),
Cn float,

)