mysql - Command to insert into with select -

i have table:

create table student(name varchar(20), surname varchar(20), age int); 

first, insert table fields:

insert student values ("jhon", "smith", null); insert student values ("mark", "william", null); 

now, how insert age=28 name = 'jhon'??

you have use update below :

update student set age = 28 name = "jhon"; 

notice : it change age of people name = "jhon"

it's far better define primary key (id) column perform commands specific id.