Before inserting check all fields present in table or not if present means exit from the method else save the data
ex:
public void save()
{
saldataadapter da=new SqlDataAdapter("select *from sample",con);
dataset ds=new dataset();
da.fill(ds);
for(int i=o;i<ds.tables[0].rows.count;i++)>
{
if(txtname.text==ds.tables[0].rows[i][1].tostring() &&txtaddr.text==ds.tables[0].rows[i][2])
{
response.write("Data exist");
}
else
{
}
}
}
or
after inserting data disable the save button
btnsave.visible=false;