Get the first N data after MySQL group query

The idea is to
query the data, and then use group by to sort, so that we can get the grouped data, and then we customize a field in the query field in select to get its sort order, and finally add a layer to the outer layer, just get The first N pieces of data are sufficient.

example

SELECT  t.*
FROM  (    
    SELECT      a.id,      
                a.type_id,      
                c.`name` AS typeName,      
                a.scan_total,      
                a.`name`,      
                (        
                    SELECT          COUNT(b.id)                
                    FROM          course AS b        
                    WHERE         b.type_id = a.type_id        
                        AND b.scan_total > a.scan_total      
                ) AS top    
    FROM      course AS a    LEFT JOIN course_type AS c     
        ON c.id = a.type_id    
    ORDER BY      a.type_id ASC,      
                  a.scan_total DESC  
) AS t
WHERE  t.top < 3