Update Custom table with data ??

Dear All,

I have a custom table with some data. now I have to add 2 more fields to that table. I made changes and it shows me no syntax errors. Now I want to activate thia table.

I wonder what happens to my old data and what will be corresponding new field value. One of my friend was saying that it will ask you to do some repair. in Which T code should I do it.

Thanks

Madhu