Add auto increment to newly added column which is null with

Question

I have a table with 11 rows variable now i am need in id column and set as primary key and i want to number or auto increment the id column for 11 rows
 
eg :
id name address
null a b
null c d
.
.
11 records
 
i want ot output like that
id name address
1 a b
2 c d
.
.
.
11 z f