Hello everyone,
New to STATA and love the helpful community I've been seeing, any help will be much appreciated.
I have a dataset with approx. 150 individuals (1 individual = 1 user id) who have completed multiple questionnaires (K10, WSAS, etc) as well as standard demographic questions like so.

Code:
* Example generated by -dataex-. For more info, type help dataex
clear
input byte(k10 assist_full wsas staging edeqtotal age gender edu relstatus supportlevel) str36 user_id
28 12 21 0 5 19 1 2 4 2 "0178caa1-ef5b-442c-acde-b34427f1e89c"
28  0 20 3 4 14 1 0 4 1 "01ef4fdb-8355-4347-b8d6-8b2856bb0339"
40  2 31 3 5 15 1 0 2 1 "02dbd31a-a1b8-4f0a-ab4f-21e58f24e823"
39 22 27 3 4 15 1 1 2 1 "06dba546-3f2a-41b4-aa8c-0d5fd16164bf"
31  8 22 3 4 15 1 0 . 1 "0744ea4c-3149-4758-95f2-af4f68f2ed00"
end
label values gender genderlabel
label values edu edugrouplabel
label def edugrouplabel 0 "Below Year 10", modify
label def edugrouplabel 1 "Year 10 - 12", modify
label def edugrouplabel 2 "Tertiary education", modify
label values relstatus relstatuslabel
label def relstatuslabel 2 "Partnered, living apart", modify
label def relstatuslabel 4 "Single", modify
label values supportlevel supportlabel
label def supportlabel 1 "Dependent on services/relatives/coinhabitants", modify
label def supportlabel 2 "Independent", modify
Seems simple enough, however, I have multiple files with more questionnaire results as well as subscores, and the problem is that not every individual completed every questionnaire. There are also some duplicates where the individual completed the questionnaire twice (user ID would be the same). When I tried to merge the datasets, I couldn't get them to match up with the correct user id. I would like to be able to add new variables (questionnaires) and observations to my main dataset so the correct scores get attributed to the same user_id, and if I use bysort the observations won't get moved around. At the moment I have been manually copy pasting in data editor and I know soon enough I will make a mistake.
Also my "user_id" variable says 0 observations when I do summarize.

All of the help I could find online is the isid commend which I don't think did anything, or generating new unique IDs within Stata (I need to use the IDs that have been given to me so no help) or generating unique IDs for every observation (again, I need the ID to be consistent per user).

Thanks so much and hope my question wasn't too silly.

Jessica