Summary of mysql data grouping usage summary

Like the title, I have also looked for related solutions on the Internet. Many of the answers are like this SQL statement: select Id,Ac count Id,Mark,max(Create Time ) as Latest from AccountMark as b group by AccountId using the Max function. But there seems to be something wrong in the data I found. As shown in the picture, in the highlighted data, the Mark field and the CreateTime field do not correspond at all! How is this going? Is it reliable to group by using the Max function? There is another statement: select *,COUNT(AccountId) as Num from (select * from AccountMark order

1. Detailed explanation of how Mysql groups data and extracts the most recent data

Introduction: Use the Max function. But there seems to be something wrong in the data I found. As shown in the picture, the Mark field and the CreateTime field do not correspond to each other at all. !

##2. mysql data grouping: Filter grouping

Introduction: In addition to grouping data using group by, MySQL also allows filtering groups to include and exclude groups. For example, you may want to list all customers with at least two orders. For this kind of data, filtering must be done based on complete groups rather than individual ones. We have already seen the role of the where clause. However, in this example where does not accomplish the task because the where filter specifies rows and not groupings. There is no concept of grouping in where

##3.

mysql data grouping and sorting and SELECT clause order

Introduction: The first difference listed in the table is extremely important. We often find that data grouped by GROUP BY is indeed output in grouping order, but this is not always the case. Well, it's not required by the SQL specification. Also, users may ask for sorting in a different order than grouping. Just because you group the data in a certain way (to get a specific grouped aggregate value), doesn't mean you need to. Order the output in the same way. An explicit ORDER BY clause should be provided, even if its effect is equivalent to the GROUP BY clause. Don't forget ORDER

##4. mysql data. Grouping: Create Grouping

# Introduction: SQL aggregate functions can be used to summarize data. Do counts, calculate sums and averages, get maximum and minimum values ​​without retrieving all data. As a reminder, all calculations so far have been performed on all data in the table or data matching a specific where clause. Example returns the number of products provided by supplier 1003

5. SQL data grouping (GROUP BY) maximum value, first item, first three examples

Introduction: The maximum value of SQL data grouping, the first one, a summary of the first three methods, the three examples are relatively simple and they can just perform some simple operations based on the data from GROUP BY, students in need You can refer to it.

6. 05. Get certain rows of data in the SQL group

Introduction: Right When grouping data in a table, sometimes you only need the aggregate value of a certain column; sometimes you need to return the entire row of data. Commonly used methods include: subquery, ROW_NUMBER, and APPLY. The overall feeling is that ROW_NUMBER is more intuitive. Test data: ) testGroup testGroup(ID ,UserID int ,OrderID int ) GO insert testGroup ,,,,,,,,, 4000

7. Learn Oracle’s complex queries step by step (Key point)

Introduction: Preface In practical applications, it is often necessary to perform complex data statistics, and often display data from multiple tables, so we must attach great importance to: complex select statements! 1-The important function of data grouping: max , min, avg, sum, count(1

##8. GROUP BY group query and SQL execution sequence

Introduction: Use GROUP BY to group data from SELECT results. You need to know some important rules before using GROUP BY. The GROUP BY clause can contain any number of columns, which means that it can be grouped in groups. , provides more granular control over data grouping. If multiple groups are specified in the GROUP BY clause, the data will be divided into the last specified one.

9. Standard PHP's AES Encryption algorithm class

Introduction: AES is a group key. The algorithm inputs 128 bits of data, and the key length is also 128 bits. Nr is used to represent the number of rounds of encryption for a data group. (The relationship between the number of encryption rounds and the key length is listed in Table 1). Each round requires an input group

##10.

Mysql data grouping takes a certain field value. All the largest record rows_MySQL

Introduction: Mysql data grouping takes all the largest record rows of a certain field value

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