1、更新titles_test表：UPDATE titles_test
2、将所有to_date为9999-01-01的全部更新：
WHERE to_date = '9999-01-01'
3、更新to_date为NULL，且from_date更新为2001-01-01：
SET to_date = NULL, from_date = '2001-01-01'
4、串联：
UPDATE titles_test
SET to_date = NULL, from_date = '2001-01-01'
WHERE to_date = '9999-01-01'