Answers for "how to apply auto increment on existing column in mysql"

insert into auto increment mysql

/* To insert into an auto incrementing field without specifing every column in
the table, you can use the key word default in the place of the auto 
incrementing column*/

INSERT INTO my_table VALUES(default, "test1", 222)
/*VS */
INSERT INTO my_table(name, num) VALUES("test1", 222)
/*Having to type out all of the column names except the auto incrementing one
can be very tedious when you have many columns, just use the keyword defualt
instead and you only have to type it once.