Yes, upsert doesn’t support FROM.
My full raw SQL query looks like:
INSERT INTO
table (field_a, field_b)
VALUES
('', ''),
('', ''),
('', '')
ON CONFLICT (field_a, field_b)
DO
UPDATE SET (field_a, field_b) = (select * from my_function(field_a, field_b, $1, $2) as (value1 uuid, value2 timestamp));


















