sql中的最大频率答案

【问题标题】：max frequency in sqlsql中的最大频率
【发布时间】：2022-01-21 11:51:18
【问题描述】：

我有 2 个表（mysql）

tbl_products
tbl_counting

我在 tbl_counting 表中收集了 3 个用户的“机架”和“库存”信息。我想用 tbl_counting 数据更新“tbl_products.rack”和“tbl_products.stock” 在这种情况下（如结果）：

每个“机架”和“库存”信息必须由至少 3 个用户收集
tbl_products.rack”和“tbl_products.stock”必须以“Rack”或“Stock”信息的最高频率（至少 2 次）更新
如果“Rack”或“Stock”信息重复少于 2 次，请使用“Unknow”指定字段。（类似结果）

谢谢

1. tbl_products（更新前）

id	product_name	rack	stock
1	apple
2	orange
3	strawberry

2。 tbl_counting

product_id	user_id	rack	stock
1	1	A-1-1	20
1	2	A-1-1	10
1	3	B-1-1	20
2	1	C-1-1	10
2	2	D-2-1	30
2	3	A-3-1	30
3	1	X-3-1	25
3	2	X-1-1	10
3	3	X-3-1	25

结果：tbl_products（更新后）

id	product_name	rack	stock
1	apple	A-1-1	20
2	orange	Unknown	30
3	strawberry	X-3-1	25

select 
tbl_counting.product_id,
tbl_counting.rack,
MAX(tbl_counting.stock),
count(*) as freq
from tbl_counting 

group by tbl_counting.product_id
having count(*) =(select max(freq) 
from (select product_id,count(*) as freq 
from tbl_counting group by product_id) tbl_counting)

【问题讨论】：

你是怎么解决这个问题的？它停在哪里？为什么停在那里？什么（确切地）出了问题？为什么别人需要解决你的（家庭）工作？
为什么apple 的库存是 20 而不是 10？两行都有A-1-1 作为rack
我们在哪里可以找到机架Unknown？

标签： mysql sql

【解决方案1】：

这是一种可能的解决方案。前两个 cte 按产品为您提供用户数和不同机架，在下一个 cte 中用于过滤符合给定条件的记录。

UPDATE tbl_products P
JOIN (
    WITH uses_count AS
    (
        SELECT product_id,              
               COUNT(DISTINCT user_id) AS num_users         
        FROM tbl_counting 
        GROUP BY product_id
    )
    , rack_count AS
    (
        SELECT product_id,   
               rack,
               COUNT(*) AS freq         
        FROM tbl_counting 
        GROUP BY product_id, rack
    )
    ,rank_result AS 
    (
      SELECT T.product_id,
             T.rack,
             T.stock,
             R.freq,
             U.num_users,                 
             ROW_NUMBER() OVER(PARTITION BY T.product_id ORDER BY R.freq DESC, T.stock DESC) AS RN
      FROM tbl_counting T
      LEFT JOIN uses_count U
        ON T.product_id = U.product_id
           AND CASE WHEN U.num_users >= 3 THEN TRUE ELSE FALSE END
      LEFT JOIN rack_count R
        ON T.product_id = R.product_id
           AND CASE WHEN R.freq >= 2 THEN TRUE ELSE FALSE END  
    )
    SELECT product_id, 
           stock,               
           CASE WHEN freq IS NULL THEN 'Unknown' ELSE rack END AS rack
    FROM  rank_result
    WHERE RN = 1) R
  ON P.Id = R.product_id
SET P.stock = R.stock,
    P.rack = R.rack

【讨论】：

您的 SQL 语法有误；检查与您的 MariaDB 服务器版本相对应的手册，以在第 34 行的“UPDATE tbl_products P JOIN rank_result R ON P.Id = R.product_id AN...”附近使用正确的语法
尝试更新的查询是否有效。
“字段列表”中的未知列“R.freq”
立即尝试。它在其中一个 ctes 中丢失。
“字段列表”中的未知列“R.c”

【解决方案2】：

你可以检查一下

SELECT
    product_id p,
    shelf,
    floor,
    line,
    stock 
FROM
    user_product 
GROUP BY
    product_id,
    stock,
    floor,
    line,
    shelf
HAVING
    stock = ( SELECT stock FROM user_product WHERE product_id = p GROUP BY stock ORDER BY count(*) DESC LIMIT 1 ) AND
    floor = ( SELECT floor FROM user_product WHERE product_id = p GROUP BY floor ORDER BY count(*) DESC LIMIT 1 ) AND
    line = ( SELECT line FROM user_product WHERE product_id = p GROUP BY line ORDER BY count(*) DESC LIMIT 1 ) AND
    shelf = ( SELECT shelf FROM user_product WHERE product_id = p GROUP BY shelf ORDER BY count(*) DESC LIMIT 1 );

【讨论】：