If your column is named brandQCDate, then remove the @
. The @
makes it a user defined variable, not the column. Also you want to make this a BEFORE UPDATE
trigger.
CREATE TRIGGER `qc_date_trigger` BEFORE UPDATE ON `brand`
FOR EACH ROW BEGIN
IF NEW.brandQC = '1' THEN
SET NEW.brandQCDate = CURDATE();
ELSE
SET NEW.brandQCDate = NULL;
END IF;
END