A.存储数据B.检索数据C.统一、安全、性能D.生成新的数据
A.select *from game where 等级>=80or 等级< =60B.select *from game where not 等级< 80or 等级< =60C.select *from game where not 等级< 80or not 等级>60D.select *from game where not 等级< 80or not 等级>=60
A.sqlyogB.mysql workbenchC.navicat