• ## Aggregate function

Time：2022-4-16

MySQL # provides many functions Count: count，frequency，nullNo statistics Max：Maximum Min：minimum value Sum：Sum Avg：average value Round：rounding   Aliases are usually given when using aggregate functions   9.6.1 countfunction ##countfunction count(*):Will not ignorenullValue of. #（1）InquiryempNumber of records in the table Select count(*) from emp;    ##(2)StatisticsempIn the table, the number of people with Commission ##count(Specific field)，nullThe value is […]

• ## [problem thinking] the difference between “multiple” and “multiple”

Time：2022-3-12

In the first learning period, we learned the preliminary understanding of “times” and the concept of “times”. In the second stage, we learn the concept of “multiple”. So are the words “times” and “multiples” the same thing? What’s the difference between the two words? “Times” is a quantitative relationship, which is based on the concept […]

• ## Groupby group combined and parallel content ~ further optimized

Time：2022-3-3

Pandas questions and answers chapter 013. Today’s article is the last one（After groupby is grouped, how to merge the contents in the column?）Supplement to, focus on recommending group friendsXiao Ming, after the last article was published, he quickly gave me three more optimized solutions, one more concise than the other. With such a good thing, […]

• ## What is the SIR epidemic model that has recently been wildly spread in statistical science?

Time：2021-12-7

Recently, I saw a picture of Sir infectious disease model posted on the Internet. Many people should not know much about this model. Let’s talk about this model today. This one is only academic, not anything else. SIR model is one of the most classical infectious disease models. There are also Si and sis. Sir […]

• ## Python crawls through the data of a down jacket and uses visualization to help you choose your favorite clothes

Time：2021-9-12

The text and pictures of this article come from the network, only for learning and communication, and do not have any commercial purpose. If you have any questions, please contact us in time for handling. The following article is attached to the study of Python by brother J Novices and Xiaobai who have just come […]

• ## Pat 1003 emergency (25 points)

Time：2021-8-27

Pat 1003 emergency (25 points) As an emergency rescue team leader of a city, you are given a special map of your country. The map shows several scattered cities connected by some roads. Amount of rescue teams in each city and the length of each road between any pair of cities are marked on the […]

• ## [linked list topic] soldier queue training

Time：2021-8-25

A unit carries out a queue training of recruits. The recruits are numbered in sequence from the beginning and lined up in a horizontal line. The training rules are as follows: report from the beginning one to two. For those who report to the second column, the rest move closer to the small sequence number, […]

• ## R language bus and subway line entry and exit data mining network diagram visualization

Time：2021-8-18

Original link:http://tecdat.cn/?p=22751 For the data mining of huge bus and subway route information, there are two main problems encountered by general software: 1. For the mining of text information, especially Chinese vocabulary, there is a lack of mature tools or software packages; 2. For a large amount of data, the reading and processing of general […]

• ## This year’s Olympic Games will be postponed to the summer of 2021. Take stock of the data of previous Olympic Games

Time：2021-6-12

The text and pictures of this article are from the Internet, only for learning and communication, and do not have any commercial use. If you have any questions, please contact us in time. The following article is from CDA data analyst, author: CDA data analyst   preface At the beginning of 2020, the sudden attack […]

• ## The accuracy of the new crown prediction model created by Chinese American little brother is far higher than that of famous universities and American official institutions

Time：2021-6-2

In 2020, with the outbreak of COVID-19, more and more people paid attention to the prediction of the number of new crown deaths. Two of the most striking models were established by Imperial College London and IHME in Seattle, USA. However, the results predicted by the two models are quite different. Imperial College London said […]

• ## PHP to achieve statistical IP number and online number

Time：2021-6-1

Original address:https://www.wjcms.net/archives/php Realize the statistics of IP number and online number Words written in the front Many people have such a demand, that is, the number of people who visit IP and online. Today, let’s take a look at the specific implementation method. Open dependent function module To achieve this function, you need to rely […]

• ## What is the latest crazy SIR Epidemic Model in statistical science?

Time：2021-2-22