Where clause query - mysql

Question

So I have query the output is supposed to show all medically trained staff and all volunteers that have first aid:
SELECT Concat (s.staff_fname, ' ', s.staff_lname) AS Staff_Name,
s.medically_trained,
s.staff_email_address,
Concat(v.volunteer_fname, ' ', v.volunteer_lname) AS Volunteer_Name,
v.first_aid,
v.volunteer_email_address
FROM volunteer v
JOIN staff s
ON v.volunteerid = s.staffid
WHERE s.medically_trained = ' yes'
AND v.first_aid = ' yes'
however when I execute my code it says empty set. What am I doing wrong?
I am a beginner coder so please dont judge if ive made an obvious mistake lol
THANK YOU!

Answer 1

First remove the space from 'yes' , it may also cause this issue.You may get the not null value in result.
If it is still blank then try to run the where clause individually on both of the tables,
Select *
FROM volunteer v where v.first_aid = 'yes';
and
select * from staff s
WHERE s.medically_trained = 'yes' ;
and check whether any one of it is giving you null as a result, if yes then your answer is correct.

Answer 2

Remove the spaces in where section:
SELECT Concat (s.staff_fname, ' ', s.staff_lname) AS Staff_Name,
s.medically_trained,
s.staff_email_address,
Concat(v.volunteer_fname, ' ', v.volunteer_lname) AS Volunteer_Name,
v.first_aid,
v.volunteer_email_address
FROM volunteer v
JOIN staff s
ON v.volunteerid = s.staffid
WHERE s.medically_trained = 'yes' /* <-- */
AND v.first_aid = 'yes' /* <-- */

Answer 3

Try this:
SELECT CONCAT(s.staff_fname,' ', s.staff_lname)AS Name,s.medically_trained AS Trained,s.staff_email_address AS Email_Address,'STAFF' cType
FROM staff s
WHERE s.medically_trained = ' yes'
UNION ALL
SELECT Concat(v.volunteer_fname, ' ', v.volunteer_lname) AS Name,v.first_aid AS Trained,v.volunteer_email_address AS Email_Address,'VOLUNTEER' cType
FROM volunteer v
WHERE v.first_aid = ' yes'
I used UNION ALL for the two table because I dont think Volunteer_ID will be Equivalent to STAFF_ID. I included cType Column for you to identify if the record was from Staff table or Volunteer

Answer 4

If you do a CONCAT('foo', 'null'), the result will be null. Check to see if that's not the case.
Also, it could be from either the JOIN clause or WHERE clause. Try running the query without JOIN and then without the WHERE clause and see if you'll still have empty sets.