-- Remove invalid record types before applying constraint
DELETE FROM dns_records WHERE record_type NOT IN ('A', 'AAAA', 'CNAME', 'TXT');

-- Now apply the constraint
ALTER TABLE dns_records DROP CONSTRAINT dns_records_record_type_check;

-- MySQL doesn't support table-level CHECK constraints, using trigger instead
DELIMITER //
CREATE TRIGGER check_record_type_before_insert
BEFORE INSERT ON dns_records
FOR EACH ROW
BEGIN
    IF NEW.record_type NOT IN ('A', 'AAAA', 'CNAME', 'TXT') THEN
        SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = 'Invalid record type';
    END IF;
END;
//
CREATE TRIGGER check_record_type_before_update
BEFORE UPDATE ON dns_records
FOR EACH ROW
BEGIN
    IF NEW.record_type NOT IN ('A', 'AAAA', 'CNAME', 'TXT') THEN
        SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = 'Invalid record type';
    END IF;
END;
//
DELIMITER ;