数据库怎么定义数值为空

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云数据库RDS MySQL版

云数据库RDS MySQL版 MySQL 是全球最受欢迎的开源数据库，阿里云MySQL版通过深度的内核优化和独享实例提供稳定极致的数据库性能，同时灵活的部署架构及产品形态，可满足不同场景下的数据库需求。

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数据库怎么定义数值为空

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