mysql - JOIN 返回表中的所有数据

Question

我的 Select 命令遇到问题，首先，我需要显示与其他表上的 idHour 不同的所有时间，代码如下:

SELECT DISTINCT Hours 
FROM agenda_hours A 
JOIN appoitment_hour B 
    ON (A.idHours <> B.Hour);

结果:

+----------+| Hours    |+----------+| 07:00    || 07:30    || 08:00    || 08:30    || 09:00    || 09:30    || 10:00    || 10:30    || 11:00    || 11:30    || 12:00    || 12:30    || 13:00    || 13:30    || 14:00    || 14:30    || 15:00    || 15:30    || 16:00    || 16:30    || 17:00    || 17:30    || 18:00    || 18:30    || 19:00    || 19:30    || 20:00    |+----------+

Answer 1

试试这个方法:

SELECT DISTINCT Hours 
FROM agenda_hours A 
LEFT JOIN appoitment_hour B 
    ON (A.idHours = B.Hour)
WHERE B.Hour is null;