null ①零，零的 ②无效的，无价值的 ③类光[的]†
null 零的；零
数据库 数据库管理系统及其实现技术 释文 null 空值
- spatial content
- spatial coordinate
- spatial coordinate transformation
- spatial correlation
- spatial correlation analysis
- spatial correlation function
- spatial crystallographic group
- spatial curve
- spatial curvilinear web
- spatial data
- spatial data access
- spatial data acquisition
- spatial data assimilation
- spatial database
- spatial database engine
- spatial database management system
- spatial database of geological map
- spatial data capture
- spatial data capture from internet
- spatial data capture from internet of things
- spatial data catalogue
- spatial data cleaning
- spatial data clearing house
- spatial data compression
- spatial data consolidation