What difference between PRIMARY KEY and AUTO_INCREMENT PRIMARY KEY ?

Question

full difference please

Answer 1

which field defined as primary key in a table, that field never contents duplicate value. Not even null value.It may AUTO_INCREMENT or not.
And AUTO_INCREMENT keyword also never insert duplicate values but the main thing is this field value is increasing automatically +1, when new row inserted.No need to input value by user.

Answer 2

auto_increment is for adding +1 on every primary key record ex: my first record of column name is Jonh,the id Will be automaticaly 1, and for thé next record,for exemple Mike,the primary key column will be 1+1= 2,for thé next recirdy,3,4,...

Answer 3

so primary key can be 1,2,4,5,6 but autoincrement primary key can be only as - 1,2,3,4,5,6 ?