Formual for weight loss

[FB1]

Have data that is recorded several time each month.
need to be able to pull out month difference

A big thank you for everyones help
I know I can put them into a detail(as there can be 10-15 different entries each month), then group on date field monthly
but I need to be able to show the weight loss or gain from the month before
only need to look at pre entries

Ralph

Required
"Pre Date","Weigth","Change/Month",BMI
06/02/2012,"100.0 ","-0.2 loss",122
11/01/2012,"100.2 ","0.0 gain",123
16/12/2011,"100.2 ","0.2 gain",122
21/11/2011,"100.0 ","-0.2 loss",124
26/10/2011,"100.2 ","-0.2 loss",125
26/09/2011,"100.4 ","1.6 gain",132

the fields are called

oid
fk_oid (patients id)
didat (Date)
Prepost ( weather a pre rec or a post record)
diwt (weight)
BMI

 

[FB1]

hi if anyone needs to know how I did this
as follows

select
oid as recid,
fk_oid as patientid,
DIDAT as date,
prepost,
DIWT as weight,
DIBPS, DIBPD, DIGAIN, DIIW, DIHEIGHT,
sp_bmi(oid) as BMI
from p_anthropometry as pa1
where prepost = '200100' and pa1.fk_oid = {?ThisPat}
and DIDAT = (
select max(pa2.DIDAT)
from p_anthropometry as pa2
where prepost = '200100' and pa2.fk_oid ={?ThisPat}
and pa2.fk_oid = pa1.fk_oid
and DATE_SUB(pa2.didat,INTERVAL (DAY(pa2.didat)-1) DAY) =
DATE_SUB(pa1.didat,INTERVAL (DAY(pa1.didat)-1) DAY)
and DATE_SUB(pa2.didat,INTERVAL (DAY(pa2.didat)-1) DAY) >=
adddate(DATE_SUB(didat,INTERVAL (DAY(curdate())-1) DAY) , -7))
order by fk_oid, didat desc limit 7