Referencing AppSetting in Select property of SqlDataSource control

Question

Hello everyone. A simple problem.... Got a SqlDataSource with a select, in this select I want to insert a value from web.config just like this

<asp:SqlDataSource ... SelectCommand="SELECT field FROM table"></asp:SqlDataSource>

well field is a value from web.config "Field" application setting

<add key="Field" value="tablename"/>

I want to reference it like this:

<asp:SqlDataSource ... SelectCommand="SELECT <%$ AppSettings:Field %> FROM table"></asp:SqlDataSource>

NO WORK!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Well, if there is something very bothering in the ASP.NET Framework, it is inline expressions. I DONT UNDERSTAND WHICH USE AND WHY SOMETIMES SOME EXPRESSIONS WORK AND THE SAME ONES DO NOT IN VERY SIMILAR CONTEXTES for example, in the ConnectionString property if I write

ConnectionString = "<%$ ConnectionStrings:MyConn %>"

IT WORKS IN THAT SAME DAMN TAG!!!!!! (I mean the SqlDataSource) Thank you