MYSQL||报错：In aggregated query without GROUP BY, expression #1 of SELECT list contains nonaggregated

Broken thoughts:

        Brother Meng, I’m back with Hu Hansan (｡･∀･)ﾉﾞ Hi, I was in the final exam recently, and I accidentally didn’t post for 20 days, and I didn’t succeed in the KPI at the end of the year, so I’ll make it up today §(* ￣▽￣*)§

1. Problem description

        Today, I am doing a SQL question on Niuke.com: Analysis of Niuke's Course Orders (5), and those who are interested in the specific content will search for it by themselves. Here is a brief description~~

        The encoding requirements are as follows:

         The code I wrote is as follows (it's an old woman's foot wrap, smelly and long, who called me a rookie? 〒▽〒

WITH base_table AS (
    SELECT user_id,date,DENSE_RANK() over (partition by user_id order by date) AS rnk
    FROM order_info
    WHERE date>'2025-10-15'
    AND status='completed'
    AND product_name IN ('C++','Java','Python')
),
table1 AS (
    SELECT user_id, date as first_buy_date
    FROM base_table
    WHERE rnk=1
),
table2 AS (
    SELECT user_id, date as second_buy_date
    FROM base_table
    WHERE rnk=2
),
table3 AS (
    SELECT user_id, COUNT(user_id) AS cnt
    FROM base_table
)
SELECT base_table.user_id,first_buy_date,second_buy_date,cnt
FROM base_table,table1,table2,table3
WHERE base_table.user_id=table1.user_id
AND base_table.user_id=table2.user_id
AND base_table.user_id=table3.user_id

        Then click on the self-test to run, and it will report an error gloriously, okay! The content is: SQL_ERROR_INFO: "In aggregated query without GROUP BY, expression #1 of SELECT list contains nonaggregated column 'base_table.user_id'; this is incompatible with sql_mode=only_full_group_by" 

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2. Reason analysis

        The error statement is simply translated as: "In an aggregate query without GROUP BY, expression 1 of the SELECT list contains the non-aggregated column 'base_table.user_id'; this is incompatible with sql_mode=only_full_group_by".

        Then we will check where the statement uses 'base_table.user_id'. It can be seen from the code that 'base_table.user_id' appears in table1, table2, table3 and the final query body;

        The error statement prompts that the group by statement is not used where the aggregate function is used . This is not talking about table3 hhh, table3 uses the count function, but does not add the group by statement.

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3. Solutions

        After analyzing the problem, you will naturally know how to solve it~~ Just add the GROUP BY statement to the table3 query statement!

         PS: Some solutions on the Internet are to directly modify the configuration file to make it compatible with sql_mode=only_full_group_by, maybe this is one of the solutions, but I am using Niuke.com for programming, and I cannot modify the configuration file o(￣┰ ￣*)ゞ It’s better to modify your code obediently

        After this post, the water post +1 ο(=•ω＜=)ρ⌒☆