Question

i recently read an article about creating secure php login system which will guide step by step and now this question camed to me why in this article there is no primary key in login_attempts table.
the article which i talked about:
this article

Create the "login_attempts" table:
CREATE TABLE `secure_login`.`login_attempts` (
  `user_id` int(11) NOT NULL,
  `time` VARCHAR(30) NOT NULL 
) ENGINE=InnoDB

please go to step 4

Create a table to store login attempts.

then the question is realy clear just as title is.is there any situation that we dont have any primary key?

Answer 1

Yes there is, but you need to atleast add a non-unique INDEX on column User_ID to improve the performance when querying on the table.

ALTER TABLE login_attempts ADD INDEX idx_userID (User_ID)

• When To Use Indexes In MySQL
• MySQL Query Optimization