📜  唯一与主键 - SQL 代码示例

📅  最后修改于: 2022-03-11 15:05:25.590000             🧑  作者: Mango

代码示例2
What is the difference between UNIQUE and PRIMARY KEY constraints? 
There should be only one PRIMARY KEY 
in a table whereas there can be
any number of UNIQUE Keys.
PRIMARY KEY doesn’t allow NULL
values whereas Unique key allows NULL values.