when i click the button in the gridview, want toshowdropdown

Question

 

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