3 tables linking by dates

[FB1]

Crystal Reports 11

MYSQL 5.2

Hi Everyone

-- HD_OBs (FK_oid is the main link this is the Patientid)
select
oid,
fk_oid,
DIDAT as HDDate,
haloc as location,
access_used

from p_anthropometry
order by didat desc;


-- HD_Prescription (FK_oid is the main link this is the Patientid)
select
oid,
fk_oid,
HWDATE,
HWOACC

from p_hdpresc
order by hwdate desc;

-- Timeline (FK_oid is the main link this is the Patientid)
SELECT oid,
fk_oid,
TXDATE,
TXMOD,
TXREAS,
TXSUPR,
TXSITE

FROM p_timeline
order by txdate desc

I have Three tables with the above fields, I will link them to a Patient table afterwards.

HD_Obs will be the main table that will have a between parameter on the date (will be pulling monthly)
I need the other tables to link to the hd_obs table but by date.

i.e yes it must go to the correct Patientid but in HD_obs the date here is the main date per row
DIDAT - FK_oid - haloc -HWDATE - HWOACC TXDATE- TXREAS
02/02/2012 - 12 -- hosp - 30/12/2011 Graft 14/01/2012- Active
01/01/2012 - 12 -- hosp - 30/12/2011 Fistula 01/01/2012 - Active


The OBsS date DIDAT is the main date, HWdate has to be older then DIDAT by at a day.
TXDate can be the same as or older than DIDAT

The dates don’t always correspond with each other, so I need to pull the nearest one below from each table

Your Help is most appreciated, I know it should links on the FK_OID then the date but please how do I write this.
Ralph