Issue With Join Doubling Results - mysql

Question

I have seen several posts about this on Stack Overflow, but none of them seems to give me an answer that I can understand.
I am trying to join several relations together in order to get all of the relevant information to output all routes that start in China and end in the United States.
In the SeaRoute relation, the start_port and end_port are stored as INT and in the Port relation the pid corresponds to the start_port and end_port and includes a pcountry column.
I am starting off with just trying to output everything that has a start_port that is in China. I am expecting 3 results from my Record relation as those are the only ones that start with China in the table; However, I am receiving 6 records at the output (all of the results appear to have been doubled if I go back and audit what's in the table).
While I want the right answer, I am more concerned that I have a fundamental misunderstanding of Inner Join and the other Join methods. What am I doing wrong?
SELECT *
FROM Record
INNER JOIN Goods AS Go_data
ON Record.gid = Go_data.gid
LEFT JOIN SeaRoute AS SR
ON Record.rid = SR.rid
RIGHT JOIN (SELECT pid, pcountry AS starting_port_country
FROM Port
INNER JOIN SeaRoute AS SR ON Port.pid = SR.start_port
WHERE Port.pcountry = 'China')
AS start_port_table ON SR.start_port = start_port_table.pid

Answer 1

From the looks of your query, you want to be INNER JOINing between the records that you have only on the routes that you want.
You know all of the SeaRoutes that start in China and end in the United States already, you do however need to join to the Ports table twice like so:
SELECT sr.rid,
sp.pcountry AS starting_port_country,
ep.pcountry AS end_port_country
FROM dbo.SeaRoute sr
INNER JOIN dbo.Port sp ON sp.pid = sr.start_port
INNER JOIN dbo.Port ep ON ep.pid = sr.end_port
WHERE sp.pcountry = 'China'
AND ep.pcountry = 'United States'
Then you just need to join that to your main query:
SELECT *
FROM Record
INNER JOIN dbo.Goods AS Go_data ON Record.gid = Go_data.gid
INNER JOIN
(
SELECT sr.rid,
sp.pcountry AS starting_port_country,
ep.pcountry AS end_port_country
FROM dbo.SeaRoute sr
INNER JOIN dbo.Port sp ON sp.pid = sr.start_port
INNER JOIN dbo.Port ep ON ep.pid = sr.end_port
WHERE sp.pcountry = 'China'
AND ep.pcountry = 'United States'
) ports ON ports.rid = Record.rid
There's no way I can explain joins to you any clearer than this page can:
https://www.codeproject.com/Articles/33052/Visual-Representation-of-SQL-Joins