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)?
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?
Primary key is always unique in every SQL. You dont have to explicitly define it as 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.
Example:
An employee details table having EmpID as Primary key and EmpPhoneNo as unique key.