What's the difference between using INDEX vs KEY in MySQL?

Question

I know how to use INDEX as in the following code. And I know how to use foreign key and primary key.

CREATE TABLE tasks ( 
  task_id INT UN         


        

Answer 1

A key is a set of columns or expressions on which we build an index.

1. While an index is a structure that is stored in database, keys are strictly a logical concept.

2. Index help us in fast accessing a record, whereas keys just identify the records uniquely.

3. Every table will necessarily have a key, but having an index is not mandatory.

Check on https://docs.oracle.com/cd/E11882_01/server.112/e40540/indexiot.htm#CNCPT721