How to join from 3 table with condition - mysql

Question

I have 3 table inside my database, my first table is person table its store all person name, my second table is hobby table its store all hobby of all person,the third table is referensi table store all references person and hobby.
Tabel person : Tabel hobby : Tabel referensi :
----------------- ------------------ -------------------------------------
| id | name | | id | hobby | | id | ref_person | ref_hobby |
----------------- ------------------ -------------------------------------
| 1 | Rose | | 1 | Makan | | 1 | 1 | 1 |
| 2 | Lisa | | 2 | Renang | | 2 | 1 | 3 |
| 3 | Jisoo | | 3 | Nyanyi | | 3 | 1 | 4 |
| 4 | Jennie| | 4 | Youtube| | 4 | 3 | 5 |
----------------- | 5 | Masak | -------------------------------------
------------------
I want to count all hobby by that person
Example I want select Rose : Or I want select Jisoo :
--------------------------- ---------------------------
| id | hobby | count | | id | hobby | count |
--------------------------- ---------------------------
| 1 | Makan | 1 | | 1 | Makan | 0 |
| 2 | Renang | 0 | | 2 | Renang | 0 |
| 3 | Nyanyi | 1 | | 3 | Nyanyi | 0 |
| 4 | Youtube| 1 | | 4 | Youtube| 0 |
| 5 | Masak | 0 | | 5 | Masak | 1 |
--------------------------- ---------------------------
And so forth, how do I solve this problem?
This is my query that I write but doesn't seem to work, because only data with count greater than 0 is shown.
SELECT
hobby.id,
hobby.name,
count( referensi.id ) AS count
FROM
referensi
LEFT OUTER JOIN hobby ON hobby.id = referensi.ref_hobby
JOIN person ON referensi.ref_person = person.id
WHERE person.id = 1
GROUP BY
hobby.id
Thanks in advance.

Answer 1

To solve this you need to JOIN referensi to person, selecting only entries in referensi corresponding to the person of interest, and then RIGHT JOIN to hobby. If there is no matching entry, the output is 0, otherwise 1. For example, for person 1:
SELECT h.id,
h.hobby,
CASE WHEN r.id IS NULL THEN 0 ELSE 1 END AS count
FROM referensi r
JOIN person p ON p.id = r.ref_person AND p.id = 1
RIGHT JOIN hobby h ON h.id = r.ref_hobby
ORDER BY h.id
This can also be implemented with a correlated subquery:
SELECT h.id,
h.hobby,
EXISTS (SELECT * FROM referensi r WHERE r.ref_hobby = h.id AND r.ref_person = 1) AS count
FROM hobby h
If a person/hobby tuple can appear in the referensi table more than once, you do need to do a COUNT:
SELECT h.id,
h.hobby,
COUNT(r.id) AS count
FROM referensi r
JOIN person p ON p.id = r.ref_person AND p.id = 1
RIGHT JOIN hobby h ON h.id = r.ref_hobby
GROUP BY h.id
Output (for all three queries on your sample data):
id hobby count
1 Makan 1
2 Renang 0
3 Nyanyi 1
4 Youtube 1
5 Masak 0
Demo on SQLFiddle

Answer 2

You can try to use condition aggravate function with OUTER JOIN
setting condition in CASE WHEN
Query 1:
SELECT
hobby.id,
hobby.name,
COUNT(CASE WHEN person.id = 3 THEN 1 END) AS count
FROM
hobby
LEFT JOIN referensi ON hobby.id = referensi.ref_hobby
LEFT JOIN person ON referensi.ref_person = person.id
GROUP BY
hobby.id,
hobby.name
Results:
| id | name | count |
|----|---------|-------|
| 1 | Makan | 0 |
| 2 | Renang | 0 |
| 3 | Nyanyi | 0 |
| 4 | Youtube | 0 |
| 5 | Masak | 1 |

Answer 3

You want to start your joining from hobby table, and use LEFT JOINs to optionnaly bring up the matching records in other tables.
SELECT
h.id,
h.hobby,
count( p.id ) AS count
FROM
hobby h
LEFT JOIN referensi r ON h.id = r.ref_hobby
LEFT JOIN person p ON r.ref_person = p.id AND p.id = 1
WHERE p.name is NULL OR p.name = 'Rose'
GROUP BY h.id, h.hobby
It is also a good practice to use table aliases, I added them to your query.
Demo on DB Fiddle for user Rose :
| id | hobby | count |
| --- | ------- | ----- |
| 1 | Makan | 1 |
| 2 | Renang | 0 |
| 3 | Nyanyi | 1 |
| 4 | Youtube | 1 |
| 5 | Masak | 0 |