Mysql: How to compare value in the same column between current day and last 7 day, is the value in current day is increase or degrade in percentage .?

Question

I have table mysql with column date, time, subject, description and value. I want to know the value at current day is increase or degrade from the value at last 7 day in the same time.

Date            Time            Subject     Description         Value|
---------------------------------------------------------------------|
2023-08-10  20:03:00    DNS Gn/BRN  DNS mem avail real   1089350|
2023-08-10  20:03:00    DNS Gn2     DNS mem total real   65601700|
2023-08-10  20:03:00    DNS Gn      DNS mem total swap   25165800|
    :         :            :              :                  :
    :         :            :              :                  :
2023-08-17  20:03:00    DNS Gn      DNS mem avail real   878044032|
2023-08-17  20:03:00    DNS Gn/BRN  DNS mem avail real   8567809|
2023-08-10  20:03:00    DNS Gn2     DNS mem total real   6780408|

The final expecting result:

Date        Time         Subject      Subject1           Value     Status|
------------------------------------------------------------------------|
2023-08-10  20:03:00    DNS Gn/BRN1 DNS mem avail real   10893500     ?|
2023-08-10  20:03:00    DNS Gn2     DNS mem total real   65601700     ?|
2023-08-10  20:03:00    DNS Gn      DNS mem total swap   25165800     ?|
    :          :            :            :                  :   |
    :          :            :            :                  :   |
2023-08-17  20:03:00    DNS Gn      DNS mem avail real   87804408   -30.84%| --> [(65601700-87804408)/65601700]
2023-08-17  20:03:00    DNS Gn/BRN1 DNS mem avail real   8567809     21.34%| --> [(10893500-8567809)/10893500]
2023-08-17  20:03:00    DNS Gn2     DNS mem avail real   6780408     75.06%|--> [(25165800-6780408)/25165800]

How to get the status of each Subject?

Meanwhile I use command LEFT JOIN, but the result was unexpected ...

Thanks