MySQL Learning record "01" PRIMARY key

The primary key is the unique identifier of the data row. Columns are not duplicated to be primary keys. A table can have no primary key, but it is very difficult to handle, so there is no special reason for the table to set the primary key.
There are two selection strategies for the primary key: the business primary key and the logical primary key. Business primary key is the use of business-meaningful field key, such as a social Security number, bank account, etc., the logical primary key is to use a field without any business meaning the key, completely to the program, the business people will not look at the data. The logical primary key is recommended because it is difficult to ensure that the business primary key is not duplicated (the ID is duplicated) and does not change (account number is raised).

MySQL Learning record "01" PRIMARY key