How to output data from iSQL to csv file _with_ headings?

I would have suggested to start with another statement:

SELECT 'ID;LASTNAME;FIRSTNAME;DOB' FROM dummy;
OUTPUT TO 'C:\\temp\\sometable.csv' FORMAT ASCII DELIMITED BY ';' QUOTE '';

and add the APPEND option on your query... but I can't get APPEND to work (but I'm using a ASA 11 engine).

Try this one

SELECT 'ID','LASTNAME','FIRSTNAME','DOB' union
SELECT string(ID),LASTNAME,FIRSTNAME,DOB FROM SomeTable;
OUTPUT TO 'C:\\temp\\sometable.csv' FORMAT ASCII DELIMITED BY ';' QUOTE '';

Simply add the option

WITH COLUMN NAMES

to your statement and it adds a header line with the column names.

The complete statement is therefore:

SELECT * FROM SomeTable; OUTPUT TO 'C:\temp\sometable.csv' FORMAT ASCII DELIMITED BY ';' QUOTE '' WITH COLUMN NAMES

See sybase documentation.