如何在特定列上不匹配的 select 行（sqlite）

Question

Ok hopefully my table works, I've never posted here before, but I'm trying to find who has received doses of more than one type of vaccine from this table (all details are dummy data, not real people or id numbers etc)

NHI_id	fname	lname	vaccine_name	vac_date
16120428	Clayton	Marsh	Comirnaty	2021-03-20
16120428	Clayton	Marsh	Janssen	2021-04-01
16120430	Dillon	Richards	Comirnaty	2021-03-20
16120430	Dillon	Richards	Comirnaty	2021-04-10
16120432	Giselle	Miles	Janssen	2021-04-15
16120433	Taylor	Buckley	Comirnaty	2021-03-20
16120434	Kermit	Greene	Janssen	2021-04-15
16120435	Harrison	Dorsey	Janssen	021-04-15

So Clayton March is the only person who has received doses of different vaccines and I'm trying show that with a query. I got the above table with the following query:

SELECT NHI_id, fname, lname, vaccine_name, vac_date
FROM Patients
NATURAL JOIN Vaccinations
NATURAL JOIN Vaccines

and I've been able to query everyone who has received two doses of any vaccine, but I'm having trouble then narrowing it down to doses of DIFFERENT vaccines.

Answer 1

Something like

SELECT NHI_id, fname, lname
FROM Patients
NATURAL JOIN Vaccinations
NATURAL JOIN Vaccines
GROUP BY NHI_id, fname, lname
HAVING count(DISTINCT vaccine_name) > 1

should do it.