How to get last 3 data of last 3 week days from a table

Question

I have a table consisting of stock market's daily data. It consists of various number of rows for each day.I have a column named 'High' in the table. Now I need to calculate MAX(High) for last 3 week days. For ex:- if today is Wednesday I need to calculate MAX of last week's friday and this week's monday,tuesday. I know that I can do this if I know the date manually using a query like this.

Select MAX(HIGH) from table_name where date>='date'

But I don't want to do like this i just want to automate this with a program written in PHP. How can i Achieve this any help in both either PHP or SQL is appreciable. My table just has 6 columns

date,time,open,high,low,close

say suppose if my table is like this

date        time       open      high     low     close
2015-05-06  09:30:00   2012.50   2020.5   2016.5  2014.0
2015-05-06  09:31:00   2013.50   2021.5   2014.5  2016.0
2015-05-06  09:32:00   2014.50   2021.75  2017.5  2013.0
2015-05-07  09:30:00   2011.50   2019.5   2018.5  2014.0
2015-05-07  09:31:00   2014.50   2022.5   2016.5  2015.0
2015-05-07  09:32:00   2012.50   2026.5   2017.5  2016.0
2015-05-08  09:30:00   2010.50   2024.5   2015.5  2017.0
2015-05-08  09:31:00   2013.50   2026.5   2017.5  2018.0
2015-05-08  09:32:00   2014.50   2028.5   2015.5  2019.0
2015-05-08  09:33:00   2014.50   2022.5   2017.5  2012.0
2015-05-11  09:30:00   2017.50   2025.5   2018.5  2013.0
2015-05-11  09:31:00   2018.50   2027.5   2019.5  2016.0
2015-05-11  09:32:00   2019.50   2024.5   2011.5  2017.0
2015-05-11  09:33:00   2020.50   2026.5   2017.5  2014.0
2015-05-12  09:30:00   2018.50   2023.5   2018.5  2018.0
2015-05-12  09:31:00   2017.50   2024.5   2017.5  2014.0
2015-05-12  09:32:00   2018.50   2023.5   2018.5  2013.0
2015-05-12  09:33:00   2017.50   2024.5   2019.5  2014.0
2015-05-12  09:34:00   2016.50   2023.5   2016.5  2012.0
2015-05-12  09:35:00   2017.50   2025.5   2018.5  2011.0

and if today's date is 2015-05-13(wednesday) I need MAX(high) of last 3 week days ie 2015-05-12,11,08 which is 2028.5.

Answer 1

Presumably, you only have data on "week days".

select max(high)
from table_name t join
     (select date
      from table_name
      group by date
      order by date desc
      limit 3
     ) dates
     on t.date = dates.date;

Presumably, you either want a condition on the stock or a group by , but this is based on your sample query.

You can make this more efficient by adding a where clause. Typically, the last three working days would be within the last week, or so:

select max(high)
from table_name t join
     (select date
      from table_name
      where date >= date_sub(curdate(), interval 7 day)
      group by date
      order by date desc
      limit 3
     ) dates
     on t.date = dates.date;

Answer 2

您可以在这种情况下使用date_sub函数：

select max(high) from table_name where date > date_sub(date, INTERVAL 3 DAY);

Answer 3

我认为这是正确的查询：

select top 3 date, max(high) from table_name order by date desc