MySql Right Outer Join with Where Clause - mysql

Question

I have 3 tables:
pd_tprofessional, pd_tpreference and pd_tprofessional_preference.
pd_tprofessional and pd_tpreference have unique id (fkprofessional and fkpreference, respectively).
pd_tprofessional_preference has 3 columns: fkpreference, patientpreference_selected, fkprofessional
What I am trying to do is write a query that will get all the all pd_tpreference and return patientpreference_selected as 1 or 0 based on if fkprofessional is 13 and pd_tprofessional_preference with that fkprofessional exists.
This is what I got so far:
SELECT patientpreference_selected, fkprofessional, pkpreference, preference_name
FROM pd_tprofessional_preference
RIGHT OUTER JOIN pd_tpreference
ON pd_tpreference.pkpreference = pd_tprofessional_preference.fkpreference
This query gives me all the pd_tpreference by right outer joining them with pd_tprofessional_preference, now I am stuck on returning patientpreference_selected as 1 or 0 based if that record exists in pd_tprofessional_preference when the fkprofessional is 13 with the fkpreference. I really hope this makes sense.

Answer 1

Conventional and easily readable way is using Left Join. You can do a left-join from the pd_tpreference table to the pd_tprofessional_preference table.
In the join ON condition, specify the condition that fkprofessional = 13.
You can use Coalesce() function to handle the case when there is no match found in the pd_tprofessional_preference table.
In multi-table queries, it is advisable to use Aliasing for code clarity and avoiding ambiguous behaviour.
Try the following:
SELECT
pref_t.fkpreference,
pref_t.preference_name,
map_t.fkprofessional,
COALESCE(map_t.patientpreference_selected, 0) AS patientpreference_selected
FROM pd_tpreference AS pref_t
LEFT JOIN pd_tprofessional_preference AS map_t
ON map_t.fkpreference = pref_t.fkpreference AND
map_t.fkprofessional = 13