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

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.