What is true about PRIMARY KEY? Choose all that apply
Can be defined on a single column or multiple columns in the table.
Can be defined only on a single column in the table.
A UNIQUE index is automatically created once PRIMARY KEY is defined on the table.
A NON-UNIQUE index is automatically created once PRIMARY KEY is defined on the table.
NOT NULL constraint is implicitly enforced on the columns which are part of the PRIMARY KEY
NULL constraint is implicitly enforced on the columns which are part of the PRIMARY KEY