Dropdown list with a "Select All" option

Question

I have three dropdown boxes, Region, District, and City. I want my District dropdown to have a "Select All" option so the user can get all Cities in the Region, else just display the City based on the selected District. My query looks like this:

IF @district =-2 THEN 
(SELECT DISTINCT city
FROM myTable
WHERE  RIGHT(Region, 3) = ?)
ORDER BY city) 
ELSE 
(select DISTINCT city
  FROM myTable WHERE District = ?)
Order by city

I'm using vb.net/sql I couldn't find any complex case scenarios in my search either. Any sugguestions would be appreciated!

Answer 1

I am not really sure what your question is, but note that the query can simplified as follows:

SELECT DISTINCT city
FROM myTable
WHERE (@district = -2 and RIGHT(Region, 3) = ?)
    or (@district <> -2 and District = ?)
ORDER BY city

Answer 2

2 ways, either append a select statement to your SQL, or add the option in the page_load using

if(!Page.IsPostBack)
{
    DropDown1.Items.Insert(0, new ListItem("Select All", 0));

}