mysql select case multiple columns as

mysql select case multiple columns as

I want to set multiple fields with something like this, how can I make it
work?
Select TableId,
CASE
WHEN StartTime > Appt THEN
Field AS Field_1
FieldId AS FieldId_1
WHEN StartTime BETWEEN Appt AND DATE_ADD(Appt, INTERVAL 1 MONTH) THEN
Field AS Field_2
FieldId AS FieldId_2
END
FROM TableA;
It doesn't work, the syntax is wrong near AS Field_1.