sql - select statement times out -

i need populate dropdown menues table contains 4 million rows.

how can without having time out on select statement?

is need sql injections. ? or else ?

now tried top 100 rows . project have lot of users , lot of details in database . need show values in dropdownlist , current code here :

protected void searchbutton_click(object sender, eventargs e) {         var search = yourseachtextbox.text.trim();         if(!string.isnullorempty(search) && search.length > 3)        {               using(sqlconnection sqlconnection = new sqlconnection("your connection string"))              {                     var query = "select top 100 * [yourtable] username @search";                      sqlcommand sqlcommand = new sqlcommand(query,sqlconnection);                      sqlcommand.parameters.addwithvalue("@search", search + "%");                }        } } 

i assume intend populate drop downs parts aof 4 million rows? have create indexes on columns separate them!

if intend populate them of contents @ once, things have timeout sure clients browsers won't handle this!