How to add a new column to table and make it pri key

[OriginalSunny]

Hi,
I am trying to add a new column to my table and making it the primary key. The problem is that i already have a primary key in the table. I cant seem to delete the column which is already the primary key and i cant seem to add the new column as i want to make it the primary key, and there is already a primary key in the table. So how do i do this??

Here is what i have tried and none of it works:

[i]alter table emp add column ID int(5) auto_increment first; (empID is the new column i want to make the new primary key)

alter table emp drop index username; (username is the present primary i want to change)[/i]

Thanks

[fenway]

Having already added the new column, you need to issue an ALTER TABLE statement with DROP PRIMARY KEY, ADD PRIMARY <yourNewCol> together, AFAIK.