How PROC SQL helps you see missing values and other data attributes

[Kels123]

I am trying to use PROC SQL left join to merge two databases. 

The first database (master) is my actual database which has rows indicating time periods during which measurements were taken for each subject; I want to keep ALL of those rows. I want to add in data from the second database (additional) based on whether "additional" has values that correspond to the time periods in each of the rows in "master". If there are no measurements in “additional” that correspond to the specified time periods, I would like for those rows to be retained as missing values, instead of dropped. For instance, for example Subject #001, I want to merge data from “additional” into the “master” database to produce the “want” database below:

Master:

StudyID	StartDate_C	EndDate1_C	Date_12mopost
001	01/04/2012	07/10/2012	01/04/2013
001	03/07/2013	06/18/2013	03/07/2014
001	06/25/2013	01/01/2015	06/24/2014

Want (desired combined database):

StudyID	StartDate_C	EndDate1_C	Date_12mopost	full_lab_Date
001	01/04/2012	07/10/2012	01/04/2013	.
001	03/07/2013	06/18/2013	03/07/2014	.
001	06/25/2013	01/01/2015	06/24/2014	07/31/2013
001	06/25/2013	01/01/2015	06/24/2014	11/22/2013

I used left join (code below), but it looks like this code is still causing rows without matches in “additional” to be dropped:

proc sql;

create table want as

select c.*, v.*

from WORK.master AS c left join WORK.additional AS v

on c.StudyID=v.StudyID_copy

where c.StartDate_C <= v.full_lab_date <= c.DATE_12MOPOST ;

;

quit;

want (using the code above, which produces something different than what I want):

StudyID	StartDate_C	EndDate1_C	Date_12mopost	full_lab_DATE
001	06/25/2013	01/01/2015	06/24/2014	07/31/2013
001	06/25/2013	01/01/2015	06/24/2014	11/22/2013

Is there a modification I can make to my code in order to get the desired outcome?

Thank you in advance.

[kiranv_ · Accepted solution]

can you change

where c.StartDate_C <= v.full_lab_date <= c.DATE_12MOPOST

to

and c.StartDate_C <= v.full_lab_date <= c.DATE_12MOPOST

[thomp7050]

Try a full join.  This will keep data where A or B exist.