How to search two tables

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C#

C#4.0

I have this tables below

Reservation Table

CheckInDate    datetime    Unchecked
CheckOutdate    datetime    Unchecked
NoOfDays    int    Unchecked
RoomId    int    Unchecked
Booking_Charges    float    Unchecked
NoOfAdults    int    Checked
NoOfKids    int    Checked

room Table

RoomId    int    Unchecked
RoomType    varchar(50)    Unchecked

on my default.aspx

I have this:

<asp:TextBox ID="TxtCheckIn" runat="server" > 
<asp:TextBox ID="TxtCheckout" runat="server" >

but it uses calendar control...

My Aim is to search the available rooms....as in to get the rooms that is not in reservation table at the particular date selected

How can i achieve that...

Thanks in advance