MySQL，获取一周中所有日子的平均值(MySQL, get averages for all days of the week)

 我有一个表格，其中包含我所在位置不可用或免费的每小时存储的数据。 我当前的查询获得一整天的平均入住/免费点数： 
 
SELECT AVG(sz.occupied), AVG(sz.free)
FROM `hourly_cache` AS sz
WHERE   sz.time BETWEEN '2017-01-01 00:00:00' AND '2017-01-02 00:00:00'
        AND HOUR(sz.time) BETWEEN 8 AND 22
        AND libID = 0
 
 但是，如果我想要的不仅仅是这一天的平均值，而是一周中的其他每一天呢？ 说：我想要本周一的平均值加周二，周三等。 
 
 我如何循环每天和每天根据它的日期运行此查询？ 
 
 我想在PHP中这样做，但想知道是否有一种方法适用于MySQL？ 

I have a table that contains data stored for every hour a spot in my location is unavailable or free. My current query gets the average occupancy / free spots of an entire day:
 
SELECT AVG(sz.occupied), AVG(sz.free)
FROM `hourly_cache` AS sz
WHERE   sz.time BETWEEN '2017-01-01 00:00:00' AND '2017-01-02 00:00:00'
        AND HOUR(sz.time) BETWEEN 8 AND 22
        AND libID = 0
 
But what if I want the average for not just this day, but every other day of the week? Say: I want the average for Monday of this week, plus Tuesday, Wednesday, etc.
 
How do I loop through each day and on each day run this query based on what day it is?
 
I was thinking of doing it in PHP but was wondering if there's an approach that works in MySQL?

原文：https://stackoverflow.com/questions/51352827