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How to get the last 3 data for the last 3 weeks from the day

I have a table consisting of daily stock market data. It consists of a different number of lines for each day. I have a column named "High" in the table. Now I need to calculate MAX (High) for the last 3 weeks. For example: if today is Wednesday, I need to calculate MAX last week on Friday and this week on Monday, Tuesday. I know that I can do this if I know the date manually using such a query.

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

But I don’t want to do this, I just want to automate this with a program written in PHP. How can I get this help in PHP or SQL. My table has a total of 6 columns

date,time,open,high,low,close

let's say my table looks 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

2015-05-13 (), MAX () 3- i.e 2015-05-12,11,08, 2028,5.

+4
3

, " ".

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;

, , group by, .

, where. , :

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;
+3

date_sub :

select max(high) from table_name where date > date_sub(date, INTERVAL 3 DAY);
+1

I think this is the correct request:

select top 3 date, max(high) from table_name order by date desc
0
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