Q:

Where clause query

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!

A:

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.

