Question

How you would go about writing a script that calculates the percent change between two values and then submit the results in to a new MYSQL table?

Answer 1

You can do it in a simple SQL query without needing to do anything in PHP at all:

Assumes table to be inserted into is called newTable and has two columns (ID which is auto_increment and percy which is the percentage value of col1/col2 from table2):

insert into newTable 
(ID, percy) 
select 
    null, 
    col1/col2 
from 
    table2 
where 
    somecondition=someOtherCondition

Or if you want to get the ID (called myID) of the original row and insert the calculated percentage into the new table:

insert into newTable 
    (ID, percy) 
    select 
        myID, 
        col1/col2 
    from 
        table2 
    where 
        somecondition=someOtherCondition