• [Mr. Zhao Qiang] index in mongodb (Part 2)


    (4) Type 3 of index: compound index Mongodb supports composite indexes, that is, multiple keys are combined to create indexes. This method is called composite index, or composite index. This method can meet the use of index in multi key value matching query. Secondly, when using a composite index, you can also use the index […]

  • Order by field of MySQL


    Series articles: Order by field of MySQL Using MySQL When we do business, we cannot avoid the sorting function. Sorting is generally usedMySQLYesORDER BYTo achieve.Order by syntax: SELECT column1, column2,… FROM tbl ORDER BY column1 [ASC|DESC], column2 [ASC|DESC],… Our usual implementations are: –ID is in ascending order. In this case, ASC can be omitted select […]

  • Java foundation — in-depth understanding of collections


    Java Foundation Set: After summarizing for a long time, it is found that it is still summarized from the perspective of interface, which is relatively clear. Therefore, this article mainly analyzes the collection from the perspective of interface* 1. Single column collection (collection interface) The collection interface is the parent interface of all single column […]

  • Recommendation: write a local search tool based on. Net – everythingtoolbar


    Open source address https://github.com/stnkl/EverythingToolbar     Software introduction Everythingtoolbar is a file search software with practical functions and small footprint. It can help users quickly and easily find the files they need in the taskbar, and improve the convenience of querying files. The software has friendly interface and simple operation. Users in need can download […]

  • In 10 hours, I shortened the running time of spark script from 15 hours to 12 minutes!


    <!– In 10 hours, I shortened the running time of spark script from 15 hours to 12 minutes! — > I was confused on Monday and wrote an article:How to fetch a specific row from Spark’s dataframe, there are several solutions to my conjecture. I didn’t expect to face this problem so soon. I use […]

  • MSSQL · query and sort the records of all tables in a database


    Reading time |0.27 minutes word count |444 characters primary coverage |1. Introduction & background “MSSQL · query and sort the records of all tables in a database” Author | SCscHero Writing time | 2021/7/13 PM10:0 Article type |Series Degree of completion |Completed motto Every great cause has a trivial beginning. 1、 Introduction & background    Completion: […]

  • SPL data structure 2-heap, maximum heap, minimum heap


    Heap is a common data structure. The bottom layer is a binary tree implemented by array. But there are no parent and child pointers. Sort according to heap properties. It is divided into minimum heap and maximum heap. Minimum heap: the value of the parent node is smaller than that of each child node Maximum […]

  • Development tips: Unicode sorting and regular matching


    brief introduction We know that computers first emerged in foreign countries. Considering the computer performance and common foreign characters at that time, ASCII was used in computers at the beginning. After all, the characters that ASCII coding can represent are limited. With the development of computers and the popularity all over the world, more coding […]

  • MySQL explain application details (hematemesis finishing)


    What is explain Using the optimizer can simulate the optimizer to execute SQL query statements, so as to know how MySQL handles your SQL statements, and analyze the performance bottlenecks of your query statements and table structures. What can explain do Sequential reading of tables Which indexes can be used Operation type of data read […]

  • Where conditional data filtering for MySQL


    Syntax: –Select * from table name where condition; Test data: –Create table statement create table `student` ( `sid` int(11) primary key auto_increment, `sname` varchar(20) not null, `sex` varchar(10) default null, `isdelete` tinyint(1) default 0 )charset=utf8; –Insert data insert into `student`(`sid`, `sname`, `sex`) values (0, ‘Dharma’, ‘male’), (0, ‘Dianwei’, ‘male’), (0, ‘Cao Cao’, ‘male’), (0, ‘Zhong […]

  • [Java from entering the pit to giving up] No 6. Tricks of array operation


    preface We have talked about the eight basic data types in Java. This article mainly talks about arrays in reference types. The main contents are as follows: Array introduction ergodic sort common method Array introduction An array is actually a collection of elements of the same data type arranged in a certain order. That is, […]

  • Five ways to query the memory occupied by the process under Linux! Who else wouldn’t?


    Article source: https://mp.weixin.qq.com/s/-kleYkSYFb39WcWR_ QRrvw Summary of methods for querying the memory occupied by processes under Linux. Suppose there is a “PHP CGI” process with a process ID of “25282”. Now you want to query the memory occupied by the process. There are many tools for viewing under the Linux command line. Now we summarize several […]