assuming, that you defined a "number"-field, the alphabetic data inserted in this type of field are ignored in operations like searching and sorting.
redefine the field as a "text"-field and the search-operation should supply the expected result.
That is exactly how I had it and what I changed it to but it still did not work. However after your comment I realised I had only changed the order number field in one table and not the other.
Thanks for your help.