How to change the SelectCommand (SQL string) of a SqlDataSource via the code behind before the page is displayed?

HiI'd like to know how to programmatically change the select statement of a SqlDataSource. I thought it would be something like this:SqlDataSource_Gymnasts.SelectCommand = "SELECT * FROM viewAllGymnastInfo"But what event would I need to add this to, and would I need anything else? I've tried many combinations, but I'm stuck! ...