duplicate record querying multiple table rows - php

Question

I have this sql to query from different tables
SELECT *
FROM `person`
LEFT JOIN person_address
ON person_address.person_id=person.person_id
LEFT JOIN address_type
ON address_type.address_type_id=person_address.address_type_id
it return this data,
It's really tedious to achieve this json format
//json
[{
"person_id":"1",
"full_name":"john",
"scores": [{
"address_type":"billing",
"address_name":"Spain"
},{
"address_type":"home",
"address_name":"USA"
}]
}]
I should fix my sql query or it's that tedious I have to do manual looping using PHP to produce the json?
Tried DISTINCT
https://i.imgur.com/tZFvKAD.png
doesn't seems to work

Answer 1

here is a supper simplified version of what I am talking about.
Given this schema ( simple Many To Many )
CREATE TABLE a(
id INT(10)
);
INSERT INTO a (id)VALUES(1);
INSERT INTO a (id)VALUES(2);
CREATE TABLE b(
a_id INT(10),
c_id INT(10)
);
INSERT INTO b (a_id,c_id)VALUES(1,1);
INSERT INTO b (a_id,c_id)VALUES(1,2);
INSERT INTO b (a_id,c_id)VALUES(2,1);
INSERT INTO b (a_id,c_id)VALUES(2,2);
CREATE TABLE c(
id INT(10),
val VARCHAR(255)
);
INSERT INTO c (id,val)VALUES(1,'one');
Now if you run this query:
SELECT
c.val AS c_val
FROM
a
JOIN b ON a.id = b.a_id
JOIN c ON b.c_id = c.id
WHERE
c.id = 1;
You will get this result
'one'
'one'
But if you run this query
SELECT
b.a_id,
b.c_id,
c.val AS c_val
FROM
a
JOIN b ON a.id = b.a_id
JOIN c ON b.c_id = c.id;
Which is just display all you will see this
a_id | c_id | c_val
1 | 1 | one
2 | 1 | one
AS seen in this DB fiddle
https://www.db-fiddle.com/f/fZnRCSXeu3wYVFzn4NBjC5/0
This is pretty clear why in this simple example, but in a more complicated case it may not be as clear. This is especially true if the where clause matches multiple rows in the last table.
Besides that you should have the key in the bridge table ( b in the above example ) set as a compound primary key on the id's from the other 2 tables.
Now the way to fix the first query is to simply add DISTINCT to it
SELECT DISTINCT
c.val AS c_val
FROM
a
JOIN b ON a.id = b.a_id
JOIN c ON b.c_id = c.id
WHERE
c.id = 1;
Now the output is
'one'
AS seen in the last query in this updated fiddle
https://www.db-fiddle.com/f/fZnRCSXeu3wYVFzn4NBjC5/1