Access5.7什么是主键？
在数据库中常常不只是一个表这些表之间也不是相互独立的不同的表之间需要建立一种关系才能将它们的数据相互沟通而在这个沟通过程中就需要表中有一个字段作为标志不同的记录对应的字段取值不能相同也不能是空白的通过这个字段中不同的值可以区别各条记录就
在数据库中常常不只是一个表这些表之间也不是相互独立的不同的表之间需要建立一种关系才能将它们的数据相互沟通而在这个沟通过程中就需要表中有一个字段作为标志不同的记录对应的字段取值不能相同也不能是空白的通过这个字段中不同的值可以区别各条记录就像我们区别不同的人每个人都有名字但它却不能作为主键因为人名很容易出现重复而身份证号是每个人都不同的所以可以根据它来区别不同的人数据库的表中作为主键的字段就要像人的身份证号一样必须是每个记录的值都不同这样才能根据主键的值来确定不同的记录
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