MySQL - Are “NOT NULL” constraints needed for primary keys?

Question

is it necessary to declare \"NOT NULL\" constraints for primary keys in the MySQL database? A primary key cannot have NULL values because it auto_increments anyway and auto

Answer 1

Primary key must not include nullable columns. auto_increment is not a check constraint, (it is rather a default constraint) , so you cannot remove not null from definition of the column that is part of primary key regardless of presence of auto_increment. You don't have to type not null while creating the table for primary key in mysql, because the engine adds this constraint automatically.