Primary key versus key

Question

When creating a mysql dump containing the structure of my database, one of the tables shows the following:

CREATE TABLE `completedTransactions` (
  `paymentId` i         


        

Answer 1

KEY is not unique, PRIMARY KEY and UNIQUE KEY are uniques.

Answer 2

Quoting the documentation of CREATE TABLE :

KEY is normally a synonym for INDEX.
The key attribute PRIMARY KEY can also be specified as just KEY when given in a column definition. This was implemented for compatibility with other database systems.

Answer 3

Yes, the KEY keyword is just an alias for the INDEX keyword.

CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name
  ...
  {INDEX|KEY} [index_name] [index_type] (index_col_name,...)
      [index_option] ...

Source: MySQL Documentation: CREATE TABLE