MySQL的：这比萨饼喜欢的客户端

Question

我有表有这样的数据：

1. John | seafood pizza 
2. Mike | pepperoni pizza 
3. Mike | pepperoni pizza 
4. John | original pizza 
5. Mike | original pizza 
6. John | seafood pizza 
7. John | pepperoni pizza 

....

我怎么能写给我造成这个这样一个查询：

John | seafood pizza 
Mike | pepperoni pizza 

如果客户对许多比萨饼有相同的数量，结果可能是任何比萨的名字。

Answer 1

我会去按用户和比萨分组计数，然后使用这个作为一个查询的数据源，找到组的最大值（使用最大连接技巧）。这并不难：

SELECT user, SUBSTRING(MAX(CONCAT(LPAD(freq, 6, '0'),pizza)),7) 
FROM 
(SELECT user, pizza, COUNT(*) AS freq 
FROM user_likes 
GROUP BY user, pizza) ilv 
GROUP BY user 

Answer 2

让我们一步一步来

以下查询会给你的次数每一个客户订购各种比萨

SELECT name, pizza, COUNT(*) AS cnt 
FROM yourTable 
GROUP BY name, pizza 

那么，我们如何获得最经常从那里订购比萨饼？我们首先要知道什么是比萨的每个客户订购的数量最多

SELECT name, MAX(cnt) AS cnt FROM (
    SELECT name, pizza, COUNT(*) AS cnt 
    FROM yourTable 
    GROUP BY name, pizza 
) AS subquery GROUP BY name 

然后使用这个号码来选择实际的比萨饼名

SELECT name, pizza, COUNT(*) AS cnt 
FROM yourTable AS t 
CROSS JOIN (
    SELECT name, MAX(cnt) AS cnt FROM (
    SELECT name, pizza, COUNT(*) AS cnt 
    FROM yourTable 
    GROUP BY name, pizza 
) AS subquery GROUP BY name 
) AS sq 
USING(name,cnt) 
GROUP BY name, pizza 

Answer 3

让我们有一个简单的解决方案：所有的 首先，我们有两列，名字和食物。 可以列出喜爱的客户的食物容易：

CREATE TEMPORARY TABLE tbltemp AS (
SELECT name, food, COUNT(*) c 
FROM food 
GROUP BY name, food 
); 

现在我们拥有所有的食物通过计数。 然后你就可以通过计数降序排列是：

SELECT * 
FROM tbltemp 
ORDER BY c DESC 

现在你有一个描述客户的喜爱列表。

UPDATE：

而是第二次查询的，取代它：

SELECT tbl1 . * 
FROM (

SELECT name, food, COUNT(*) c 
FROM food 
GROUP BY name, food 
) AS tbl1, (

SELECT name, food, COUNT(*) c 
FROM food 
GROUP BY name, food 
) AS tbl2 
WHERE tbl1.c = tbl2.c 
AND tbl2.name = tbl1.name 
AND tbl2.food = tbl1.food 
AND tbl1.c = (
SELECT c 
FROM tbltemp 
ORDER BY c DESC 
LIMIT 1) 

此查询结果是你的问题的目标。