mysql使select值默认为正整数

Question

num_daysopen返回自开放日期以来的天数。 剩余天数返回用户关闭某些内容的天数（从开放日期起最多28天）。如果超过28天days_left需要默认为0而不是-5或-15等

SELECT
  DATEDIFF(DATE(NOW()), DATE(dateopened)) AS num_daysopen,
  (28 - DATEDIFF(DATE(NOW()), DATE(dateopened))) as days_left
FROM table

Answer 1

使用GREATEST（）。

SELECT
  DATEDIFF(DATE(NOW()), DATE(dateopened)) AS num_daysopen,
  GREATEST(0,(28 - DATEDIFF(DATE(NOW()), DATE(dateopened)))) as days_left
FROM table