If I define a column as a primary key in MySql, is it also unique key by default or do I need to also define it as unique key (in case I want it to be unique)?
如果我在MySql中将列定义为主键，默认情况下它是否也是唯一键还是我还需要将其定义为唯一键（如果我希望它是唯一的）？
I saw this question What is the difference b/w Primary Key and Unique Key that explain the difference between the two but doesn't exactly answer my question. Does PK is UK by default or I need to explicitly define it.
我看到了这个问题b / w主键和唯一键有什么区别，它解释了两者之间的区别，但没有完全回答我的问题。默认情况下PK是UK还是我需要明确定义它。
2 个解决方案
#1
21
Primary key is always unique in every SQL. You dont have to explicitly define it as UNIQUE.
主键在每个SQL中始终是唯一的。你不必明确地将它定义为UNIQUE。
On a side note: You can only have onePrimary key in a table and it never allows null values. Also you can have only one primary key constraint in the table(as the point of creating a primary key is to uniquely identify the row in your table) but you can more than one unique key constraint in your table.
注意：在表中只能有一个主键，它永远不会允许空值。此外，表中只能有一个主键约束（因为创建主键的目的是唯一标识表中的行），但表中可以有多个唯一键约束。
Example:
例：
An employee details table having EmpID as Primary key and EmpPhoneNo as unique key.
员工详细信息表，其中EmpID为主键，EmpPhoneNo为唯一键。
#2
3
Primary key is always unique by definition. Not only in MySQL. So you don't need any additional unique key.
根据定义，主键始终是唯一的。不仅在MySQL中。所以你不需要任何额外的唯一密钥。
#1
21
Primary key is always unique in every SQL. You dont have to explicitly define it as UNIQUE.
主键在每个SQL中始终是唯一的。你不必明确地将它定义为UNIQUE。
On a side note: You can only have onePrimary key in a table and it never allows null values. Also you can have only one primary key constraint in the table(as the point of creating a primary key is to uniquely identify the row in your table) but you can more than one unique key constraint in your table.
注意：在表中只能有一个主键，它永远不会允许空值。此外，表中只能有一个主键约束（因为创建主键的目的是唯一标识表中的行），但表中可以有多个唯一键约束。
Example:
例：
An employee details table having EmpID as Primary key and EmpPhoneNo as unique key.
员工详细信息表，其中EmpID为主键，EmpPhoneNo为唯一键。
#2
3
Primary key is always unique by definition. Not only in MySQL. So you don't need any additional unique key.
根据定义，主键始终是唯一的。不仅在MySQL中。所以你不需要任何额外的唯一密钥。