Question

I have searched S.O. for this answer and have came close to an answer but still not close enough. I am interested in knowing if MySQL has this capability.

I have developed in Perl and MySQL 4 and I’m on MySQL 4 now.
My table looks like this…

• symbol varchar(25)
• todayDate date
• interest int(11)

My problem is this…..these symbols (about 200,000 of them) update everyday with a new number for the interest field.

An example would be this….

symbol  | todayDate  | interest
-------------------------------
A202015 | 2010-10-26 | 150
A202015 | 2010-10-25 | 100

Ideally what I would be able to do would be to update another field at the end with a percentage change from the previous record. The above would then look like this….

symbol  | todayDate  | interest | change
-----------------------------------------
A202015 | 2010-10-26 | 150      | 50
A202015 | 2010-10-25 | 100

I didn’t think that this functionality was possible in MySQL. I have come to the conclusion that I just need to grab the previous record info, do the math and then update the latest record with the percentage info. I just thought I would double check and see if any MySQL geniuses had any wisdom to pass my way.

Answer 1

After an email conversation with Ms. Wilkie, it turns out she wanted a percent change like this:

update t_test_1 as t1 
    set chng = (t1.interest - (
            select interest from (
                select *
                from t_test_1 as t11 
                ) as x
            where x.symbol = t1.symbol and x.todayDate < t1.todayDate 
            order by x.todayDate desc
            limit 1
            )) / 
            (
                select interest from (
                    select *
                    from t_test_1 as t11 
                ) as x2
                where x2.symbol = t1.symbol and x2.todayDate < t1.todayDate 
                order by x2.todayDate desc
                limit 1
            ) * 100 ;