Query returning nothing

[Schillers]

SELECT TblCaravanBooking.[Booking Ref]
FROM TblCaravanBooking
WHERE ([Forms]![Booking History]![Caravan_No] = [TblCaravanBooking].[Caravan No]);

Is returning nothing?

 

[jzwp22]

Here are some questions that might help you get to a solution:

Are you inputting the caravan number exactly at it appears in the table?
Are you entering a carriage return, enter or tab after inputting the caravan number?
Are you keeping the booking history form open as you run the query?
Are all field, table and control names spelled correctly?