mysql使选择值默认为正整数

Question

num_daysopen 返回自打开日期以来的天数。 剩余天数返回用户必须关闭某项内容的天数(距离打开日期最多有 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