when i click the button in the gridview, want toshowdropdown

In database records as follows

Room Course

11 EFA

12 RFA

13 MFA

14 ROC

Gridview as follows

Room Course

11 Button1

12 Button2

13 Button3

14 Button4

for each room i place the Button inside the gridview, when i click the each Button i want to pop up the dropdownlist,in that dropdownlist values are to be retireved from the database. for each room course are assigned that i mentioned as above.

so when i click the button display the dropdownlist,select the course that course to be postion into the partiuclar room in the gridview.

for that how can i do using csharp.

note it is web application in asp.net using C#.
Rgds,

Rao