Combining UNION ALL and ORDER BY in Firebird

Question

This is my first attempt at answering my own question, since someone may well run into this and so it might be of help. Using Firebird, I want to combine the results of two

Answer 1

Field names are not required to be equal. That's why you can't use the field name in the order by.
You may use the field index instead. As in:

(select C1, C2, C3 from T1)
union all 
(select C7, C8, C9 from T2)
order by 3