mySQL:每种类型仅显示 4 条记录，按类型分组

Question

我有 2 列名称和类型:

Name    | Type
==================
sam     | Blue  
john    | red  
jones   | Blue  
troy    | red  
dan     | red  
ben     | Blue  
joy     | Blue  
jim     | green  
tom     | red  
edi     | green  
frank   | green  
tony    | green  
jimmy   | red  

如何使用 mySQL 为每个类型提取 4 行，按类型分组，按类型排序？
我的最终结果应该如下所示:

Name    | Type
==================
sam     | Blue   
jones   | Blue  
ben     | Blue  
joy     | Blue 
edi     | green  
frank   | green  
tony    | green  
jim     | green  
john    | red     
troy    | red  
dan     | red  
tom     | red  

Answer 1

我建议有两种选择:

A) 使用 MyISAM 引擎并应用自动增量功能，但这涉及使用额外的表来进行临时存储:

CREATE TEMPORARY TABLE UserLikes(
Type varchar(20) ,
name varchar(20),
ranking int AUTO_INCREMENT,
likes int,
PRIMARY KEY ( type, ranking  )
) ENGINE=MyISAM;

INSERT INTO UserLikes
SELECT 
Type,
Name,
null AS ranking,
count(*) AS likes
FROM 
YourTable
GROUP BY Type, Name 
ORDER BY Type, likes DESC;

SELECT * FROM UserLikes WHERE ranking <= 4;

B) 另一种方式不需要任何权限，除了选择访问权限 授予，但随着表增长得太多，它会挂起:

SET @ranking = 0;
SET @currType = space(20);

SELECT 
    Types,
    Name,
    @ranking := IF( Type != @currType , 0 , @ranking + 1 ) AS ranking,
    @currType := Type,
    likes    
 FROM
(
   SELECT 
       Type,
       Name,
       null AS ranking,
       count(*) AS likes
   FROM 
       YourTable
   GROUP BY Type, Name,
   ORDER BY Type, likes DESC
) AS staging
HAVING ranking <= 4
;

我希望这对你有帮助。