Extracting all records using a conditional SQL Server query? - sql-server

Question

I have a long database of observations for individuals. There are multiple observations for each individual, all assigned different medcodeid's.
I want to extract all records of individuals with certain medcodeid's assigned, but only if they at some point have had a smaller list of specific codes assigned.
This is an example of what I start with:
long dataset, multiple observations
and this is the records I'd like to extract:
multiple observations, but patients 3 and 5 are not extracted, as they never had a medcode 12
Would this be an additional WHERE clause? I am struggling as this will then only extract the second AND medcodeid list. But I want it to extract all, if the individual has had one of these certain fewer codes at some point. I hope that makes some sense. I am unfamiliar with IF command? And cannot see how CASE WHEN would work either.
Thank you very much in advance!

Answer 1

You definitely don't want to filter out all the rows so you're right that an additional condition won't help with that. And where only lets you look at the current row and you're trying to make a decision based all the rows belonging to the patient.
This query just uses a table expression and an analytic count() that tags each row with the number of matches as it lets you look outside the current row just like you need.
-- my additions to your query are in lowercase
with data as (
SELECT obs.patid, yob, obsdate, medcodeid,
count(case when medcodeid IN (<list of mandatory codes>) then 1 end)
over (partition by obs.patid) as medcode_count
-- assuming the relationship looks something like this
from obs inner join medcode on medcode.patid = obs.patid
WHERE medcodeid IN (<list of codes>)
AND obsdate BETWEEN '2004-12-31' AND GETDATE()
AND patienttypeid = 3 AND acceptable = 1 AND gender = 2
AND YEAR(obsdate) - yob > 15 AND YEAR(obsdate) - yob < 45
)
select * from data where medcode_count > 0;
At first I thought you were requiring that at least five of the codes from the full set were found. Now that you've edited the question I believe that you want to require that at least one code from a smaller subset is present. Either way this approach will work.

Answer 2

If I'm understanding what you're asking, I think what you need is an additional WHERE clause with a subquery. This could be done with and EXIST or a join but I find an IN query to be easier to work with.
You left the FROM out of your query so I had to guess at it but try this:
SELECT
obs.patid,
yob,
obsdate,
medcodeid
FROM
obs
WHERE
medcodeid IN (list of 20 codes)
AND (obsdate BETWEEN '2004-12-31' AND GETDATE())
AND patienttypeid = 3
AND acceptable = 1
AND gender = 2
AND ((YEAR(obsdate))-yob) > 15
AND ((YEAR(obsdate)) - yob) < 45
AND obs.patid IN (
SELECT
obs.patid
FROM
obs
WHERE
medcodeid IN (5 of the 20 codes)
);