Re: any way to "ignore" a value in an INSERT/UPDATE query?

[Rick James]

I would load the new data in a temp table, then do three batch operations:

Copy in 'new' rows:
INSERT INTO TABLE ... SELECT ... FROM tmp LEFT JOIN tbl ON ... WHERE .. IS NULL;
Update those that have both a and b:
UPDATE tbl JOIN tmp ON ... SET tbl.b = tmp.b, tbl.a = tmp.a WHERE tmp.a IS NOT NULL
Update those that have just b:
UPDATE tbl JOIN tmp ON ... SET tbl.b = tmp.b WHERE tmp.a IS NULL;

(If your PKey is AUTO_INCREMENT, have you noticed that some values are being 'burned' by IODKU?)