Add an column key on an existing table

[francois chiausa]

Hello,

I have to modify a data table on a web site.
this table is use to collect selling demand so I can not stop the DB.
I need to add a column with auto increment and unique settings and then to update the data to feet the new table structure.
is there a way to do it without stoping the DB ?
or do I have to stop my web site and to modify my DB and then to update the data inside ?

thanks

TchouA