> The problem is that using the EXTERNAL FILE to declare a table doesn't
> allow the option of interpreting blanks as NULLs, nor does setting a
> field to NULL in an external file actually set it to NULL, and hence
> I'd like to create a (yes, temporary) table to copy the data from the

external

> file table, perform the necessary processing and then place the data
> into the new tables.

Because you are using Firebird 1.5, you do not need temporary table
for this task; just use NULLIF function to convert blank to NULL
when copying data from external table to new table.

Ivan