A PRIMARY KEY constraint automatically has a UNIQUE constraint. -- However, you can have many UNIQUE constraints per table, but only one PRIMARY KEY constraint per table ...

A PRIMARY KEY constraint automatically has a UNIQUE constraint. However, you can have many UNIQUE constraints per table, but only one PRIMARY KEY constraint per table.

MYSQLi stands for MYSQL Improved ... sql = "CREATE TABLE users ( id INT(6) UNSIGNED AUTO_INCREMENT PRIMARY KEY, name VARCHAR(50) NOT NULL, email VARCHAR(50) UNIQUE, age INT(3) CHECK (age ...