Join nested relationship as columns - mysql

Question

I need some help with my SQL. I am attempting to get the following rows...
ID
Sender
Code 1
Code 1 Score
Code 2
Code 2 Score
1
John Doe
AB
80
BA
87
2
Jane Doe
CD
45
DC
99
The code columns are the hard part. This is the relationships
Conversation -> Messages -> Highlights -> Codes.
Messages have a conversation_id
Messages Highlights have a message_id
Codes have a highlight_id
One conversation has many messages, Each Message has many Highlights, and any highlights have many codes.
SELECT
conversations.id,
CONCAT(senders.first_name, ' ', senders.last_name) as 'Sender Name'
conversations.created_at AS 'Start Date',
FROM
conversations
LEFT JOIN users AS senders ON sender.id = conversations.participant_1
LEFT JOIN users AS recipient ON recipient.id = conversations.participant_2
GROUP BY
conversations.name
I cannot figure out how to include the codes into the results as columns that a paired (Code 1 Name, Code Score).
The above query works to get the first few columns, but I'd like to join in the codes. Any help would be appreciated.

Answer 1

I have an idea to make use of row_number to create multiple columns
SELECT m.highlight_id,
MAX( CASE WHEN RN = 1 THEN m.code_name ELSE '' END ),
MAX( CASE WHEN RN = 1 THEN m.code_score ELSE '' END ),
MAX( CASE WHEN RN = 2 THEN m.code_name ELSE '' END ),
MAX( CASE WHEN RN = 2 THEN m.code_score ELSE '' END ),
MAX( CASE WHEN RN = 3 THEN m.code_name ELSE '' END ),
MAX( CASE WHEN RN = 3 THEN m.code_score ELSE '' END ),
MAX( CASE WHEN RN = 4 THEN m.code_name ELSE '' END ),
MAX( CASE WHEN RN = 4 THEN m.code_score ELSE '' END ),
MAX( CASE WHEN RN = 5 THEN m.code_name ELSE '' END ),
MAX( CASE WHEN RN = 5 THEN m.code_score ELSE '' END )
FROM
(
SELECT
b.highlight_id, b.code_name, b.code_score, (CASE WHEN #T = b.highlight_id THEN #RN := #RN + 1 ELSE #RN := 1 END ) AS RN, #T := b.highlight_id
FROM highlights a
JOIN codes b ON a.highlight_id = b.highlight_id
JOIN (SELECT #T := '', #RN := 0) u
ORDER BY a.highlight_id, b.code_name
) m
GROUP BY m.highlight_id
;
If you are using MySQL 8.0, it's simpler
SELECT m.highlight_id,
MAX( CASE WHEN RN = 1 THEN m.code_name ELSE '' END ),
MAX( CASE WHEN RN = 1 THEN m.code_score ELSE '' END ),
MAX( CASE WHEN RN = 2 THEN m.code_name ELSE '' END ),
MAX( CASE WHEN RN = 2 THEN m.code_score ELSE '' END ),
MAX( CASE WHEN RN = 3 THEN m.code_name ELSE '' END ),
MAX( CASE WHEN RN = 3 THEN m.code_score ELSE '' END ),
MAX( CASE WHEN RN = 4 THEN m.code_name ELSE '' END ),
MAX( CASE WHEN RN = 4 THEN m.code_score ELSE '' END ),
MAX( CASE WHEN RN = 5 THEN m.code_name ELSE '' END ),
MAX( CASE WHEN RN = 5 THEN m.code_score ELSE '' END )
FROM (
SELECT b.highlight_id, b.code_name, b.code_score, ROW_NUMBER() OVER(PARTITION BY b.highlight_id ORDER BY b.code_name) RN
FROM highlights a
JOIN codes b ON a.highlight_id = b.highlight_id
) m
GROUP BY m.highlight_id
;