• How to increase the number of network connections in CentOS


    CentOS uses external access by default, and the total number of TCP links initiated is less than 28232. It can be calculated by the result of the following command $ cat /proc/sys/net/ipv4/ip_local_port_range What I get here is: 32768 60999 The subtraction of the two is equal to 28231, which means that the number of external […]

  • C practical exercise topic 21 – monkeys eat peaches


    Title:Monkey eat peach problem: the first day the monkey picked a number of peaches, immediately ate half, not addicted, and ate one more 
 the next morning, he ate half of the remaining peaches, and another one. I ate half and one of the leftovers of the previous day every morning. When I wanted to […]

  • One second minesweeping


    You can directly use CE to modify the total number of mines. The following is the memory address of the total number of mines directly modified through C ා /// PROCESS_ALL_ACCESS -> (STANDARD_RIGHTS_REQUIRED | SYNCHRONIZE | 0xFFF) public const int PROCESS_ALL_ACCESS = (STANDARD_RIGHTS_REQUIRED| (SYNCHRONIZE | 4095)); /// STANDARD_RIGHTS_REQUIRED -> (0x000F0000L) public const int STANDARD_RIGHTS_REQUIRED = […]

  • Grouping data


    1 Introduction Data is returned in groups, not in the type of where 2 create group by select vend_id, count(*) as num_prods from products group by vend_id; 2.1 analysis Press vend_ The ID field is grouped, and then the total number is counted and the data is returned 3 filtering grouping (having) select cust_id, count(*) […]

  • MySQL Performance Optimization: why is your count (*) so slow


    How to implement countDifferent storage engines in MySQL have different ways to implement the count function.The MyISAM engine stores the total row number of a table on the disk. Therefore, when executing count (*), it will directly return this number, which is very efficient (there is no where query condition).The InnoDB engine does not directly […]

  • Stream series (13) groupingby method


    grouping Video Explanation https://www.bilibili.com/video/av78225682/EmployeeTestCase.java package com.example.demo; import lombok.extern.log4j.Log4j2; import org.junit.Test; import java.util.List; import java.util.Map; import java.util.stream.Collectors; @Log4j2 public class EmployeeTestCase extends BaseTestCase { @Test public void groudBy(){ //Get employee list based on salary Map<Double,List<Employee>> map = list.stream() .collect(Collectors.groupingBy(Employee::getSalary)); System.out.println(“map:”+map); //Get the number of employees according to salary Map<Double,Long> map2 = list.stream() .collect(Collectors.groupingBy(Employee::getSalary,Collectors.counting())); System.out.println(“map2:”+map2); //Get the […]

  • C ා complete record of steps for simple operation of mongodb


    preface Mongodb is a high-performance, open-source, modeless non relational database product written by C + +, which is the database with the most abundant functions and the most like relational database. It extends many functions of relational database, such as auxiliary index, range query, sorting, etc. Mongodb mainly solves the problem of access efficiency of […]

  • Statistical analysis of game log (1)


    Statistical analysis of game log (1) Taking the game settlement log as an example, this paper shows the process of statistical analysis of the log by using ksql. Start inclusive cd ~/Documents/install/confluent-5.0.1/ bin/confluent start View the list of Kafka topics bin/kafka-topics –list –zookeeper localhost:2181 Create a topic to accept the game settlement log bin/kafka-topics –create […]

  • TP SQL statistics query syntax


    Get today’s order total and order total //Fields distinguish the order whose order type is not equal to 1, and the order amount is money and freight $fields = [ ‘COUNT(1) as order_num’, ‘SUM(IF(order_type != 1, money + order_freight, 0)) as order_price’ ]; //Where is the payment status of today’s order $where = [ [ […]

  • Smartforms set the table footer to display on the last page


      When you print a purchase order, a total amount is calculated at the end, but when there are multiple pages, the total is displayed on each page. Now you want the total to be displayed only in the last row of the table. Smartforms adjust the table, put the total in the footer, and […]