摘要： 转载数据准备createtablestudent( snovarchar2(10)primarykey, snamevarchar2(20), sagenumber(3), ssexvarchar2(5));createtableteacher(tnovarchar2(10)primarykey,tnamevarchar2(20));createtablecourse( cnovarchar2(10), cnamevarchar2(20), tnovarchar2(20), constraintpk_courseprimarykey(cno,tno));createtablesc( snova 阅读全文