MySQL分組排序求Top N

表結構

 

按照grp分組，按照num排序，每組取Top 3，輸出結果如下：

 

 

源代碼：

SELECT * FROM score AS t3 
WHERE ( 
	SELECT COUNT(*) FROM score AS t1 
	LEFT JOIN score AS t2 
	ON t1.grp = t2.grp AND t1.num < t2.num 
	WHERE t1.id = t3.id
) < 3
ORDER BY t3.grp ASC, num DESC

 

在where中可以通過子查詢創造一個新的變量來過濾。