MySQL datetime、date、time、之間的轉化與比較

SELECT NOW(),CURDATE(),CURTIME(),
  -- datetime 轉 date time
  NOW(), DATE(NOW()), TIME (NOW()), CONCAT(DATE(NOW()), ' ', TIME (NOW())),
  -- str 轉 datetime date time
  str_to_date('2019-04-25 08:50:00', '%Y-%m-%d %H:%i:%s'),DATE('2019-04-25 08:50:00'),TIME ('2019-04-25 08:50:00'),
  str_to_date('2019-04-25 08:50:00', '%Y-%m-%d %T'),
  -- 比較
  NOW() = CONCAT(DATE(NOW()), ' ', TIME (NOW())),
  DATE(NOW()) = '2019-04-25',
  NOW() = DATE(NOW()),
  NOW() = TIME (NOW());