LIMIT number of rows in a JOIN between MySQL tables - mysql

Question

What I have
I have the following two tables in a MySQL database (version 5.6.35).
CREATE TABLE `Runs` (
`Name` varchar(200) NOT NULL,
`Run` varchar(200) NOT NULL,
`Points` int(11) NOT NULL
) DEFAULT CHARSET=latin1;
INSERT INTO `Runs` (`Name`, `Run`, `Points`) VALUES
('John', 'A08', 12),
('John', 'A09', 3),
('John', 'A01', 15),
('Kate', 'A02', 92),
('Kate', 'A03', 1),
('Kate', 'A04', 33),
('Peter', 'A05', 8),
('Peter', 'A06', 14),
('Peter', 'A07', 5);
CREATE TABLE `Users` (
`Name` varchar(500) NOT NULL,
`NumberOfRun` int(11) NOT NULL
) DEFAULT CHARSET=latin1;
INSERT INTO `Users` (`Name`, `NumberOfRun`) VALUES
('John', 2),
('Kate', 1),
('Peter', 3);
ALTER TABLE `Runs`
ADD PRIMARY KEY (`Run`);
What is my target
John have Users.NumberOfRun=2, so I will extract the 2 top records from Runs table
Kate have Users.NumberOfRun=1, so I will extract the 1 top record from Runs table
Peter have Users.NumberOfRun=3, so I will extract the 3 top records from Runs table
I would like to came to the following result
+-------+-----+--------+
| Name | Run | Points |
+-------+-----+--------+
| John | A01 | 15 |
| John | A08 | 12 |
| Kate | A02 | 92 |
| Peter | A06 | 14 |
| Peter | A05 | 8 |
| Peter | A07 | 5 |
+-------+-----+--------+
What I have tried
First of all, if it was SQL Server I would use ROW_NUMBER() OVER (PARTITION BY ... ORDER BY ) AS [rn] function to the Runs table and then make a JOIN with the Users table on Users.NumberOfRun<=[rn].
I have read this document but it seems that PARTITONING in MySQL it is available since version 8.X, but I am using the 5.6.X version.
Finally, I have tried this query, based on this Stackoverflow answer:
SELECT t0.Name,t0.Run
FROM Runs AS t0
LEFT JOIN Runs AS t1 ON t0.Name=t1.Name AND t0.Run=t1.Run AND t1.Points>t0.Points
WHERE t1.Points IS NULL;
but it doesn't give me the row number, which is essentially for me to make a JOIN as described above.
SQL Fiddle to this example.

Answer 1

A combination of 'group_concat' and 'find_in_set', followed by the filtering using the position returned by 'find_in_set' will do the job for you.
GROUP_CONCAT will sort the data in descending order of points first.
GROUP_CONCAT(Run ORDER BY Points DESC)
FIND_IN_SET will then retrieve the number of rows you want to include in the result.
FIND_IN_SET(Run, grouped_run) BETWEEN 1 AND Users.NumberOfRun
The below query should work for you.
SELECT
Runs.*
FROM
Runs
INNER JOIN (
SELECT
Name, GROUP_CONCAT(Run ORDER BY Points DESC) grouped_run
FROM
Runs
GROUP BY Name
) group_max ON Runs.Name = group_max.Name
INNER JOIN Users ON Users.Name = Runs.Name
WHERE FIND_IN_SET(Run, grouped_run) BETWEEN 1 AND Users.NumberOfRun
ORDER BY
Runs.Name Asc, Runs.Points DESC;