Tag:Wang Wu

  • Mongodb database

    Time:2021-5-30

    Mongodb It’s a non relational database. It’s stored in the form of key value pair horizontal expansion. It’s easy to use as a cache database Mongodb’s stored document is called bson, which is similar to JSON object. Field values can contain other documents, arrays and document arrays Concept analysis of mongodb and MySQL SQL concept […]

  • JS toolkit written with TS

    Time:2021-4-11

    js-util-plus 1、 Introduction Common tool classes written with typescript Every time you write a project, you need to write some duplicate tool classes, so encapsulate some commonly used tool classes. 2、 How to use yarn add js-util-plus / npm install js-util-plus –dev import * as util from ‘js-util-plus’; 3、 Cases Because it’s written in TS, […]

  • How SQL server converts data into columns and columns through pivot

    Time:2021-2-4

    script: /* Description: how SQL server converts data into columns and columns through pivot Script source: https://www.cnblogs.com/zhang502219048/p/12933347.html */ create table #t ( [employee ID] nvarchar (50), [employee name] nvarchar (50), [month] nvarchar (50), [salary] int ) insert into #t Values (n’01 ‘, n’zhang San’, n’january 2020 ‘, 2400) (n’02 ‘, n’lisi’, n’january 2020 ‘, 3000) […]

  • Functions used in total and subtotal in Oracle

    Time:2021-2-3

    @[TOC] (total and subtotal, line by line summation)###1、 Total and subtotal functions#### 1、rollupGroup by, as we all know, is a grouping function used to group a column.But when it’s used with other functions, it’s like a couple of boys and girls, hitting a different spark.==Rollup (field 1, field 2,…)Rollup and group by can be used […]

  • Reordering method of SQL

    Time:2020-11-11

    — Id Name Course Score –1001 Li Si English 100 –1007 Wang Wu mathematics 30 –1004 Li Si mathematics 62 –1005 Li Siyu 83 –1006 Wang Wu Chinese 55 –1008 three English 64 –1003 Wang Wu English 56 –1002 Zhang San mathematics 93 –1000 copies of three languages 81 –First sort according to the name […]

  • After SQL Server grouping, each group takes out any row

    Time:2020-10-21

    Data source: INSERT INTO [dbo].[dept] ([id], [code], [name]) VALUES (N’1′, N’HEX_ 1 ‘, n’ Zhang San ‘)GOGOINSERT INTO [dbo].[dept] ([id], [code], [name]) VALUES (N’2′, N’HEX_2′, N’lisi’)GOGOINSERT INTO [dbo].[dept] ([id], [code], [name]) VALUES (N’3′, N’HEX_3′, N’wangwu’)GOGOINSERT INTO [dbo].[dept] ([id], [code], [name]) VALUES (N’4′, N’HEX_1′, N’zhangsan’)GOGOINSERT INTO [dbo].[dept] ([id], [code], [name]) VALUES (N’5′, N’HEX_ 2 ‘, n’rees’)GOGOINSERT […]

  • Review of JDBC programming

    Time:2020-8-1

    1. Prepare the data –Create database CREATE DATABASE mybatis; –Using databases USE mybatis; –Delete table DROP TABLE IF EXISTS user; –Create table CREATE TABLE `user` ( `id` int(11) NOT NULL auto_increment, `Username ` varchar (32) not null comment ‘user name’, `Birthday ` datetime default null comment ‘birthday’, `Sex ` char (1) default null comment ‘gender’, […]

  • Sorting based on a field in a two-dimensional array in PHP

    Time:2020-4-15

      In order to sort a field in a two-dimensional array, you can usually do it through array circular comparison. A simpler method is introduced here, which is implemented directly through PHP functions.Array_multisort(): it can be used to sort multiple arrays at one time, or to sort multi-dimensional arrays according to one or more dimensions.For […]

  • Es basic knowledge points – (type part)

    Time:2020-4-8

    Variable type Type classification and judgment of JS Value types and references Prototype and prototype chain (inheritance) Definition of prototype and prototype chain Inheritance writing Scope and closure Execution context this What is a closure asynchronous Synchronous vs asynchronous Asynchronous and single threaded Front end asynchronous scenario Review of the new ES6 / 7 standard […]

  • Learning and using JSON

    Time:2020-2-28

    Official account: Xiao Li is not bald, Java original blogger. It will take about 7.8 minutes to read this article Preface In the process of software development, services and services call each other. Before data transmission, we usually convert the data to JSON format for transmission, such as Ajax call request, receiving the JSON data, […]

  • Learn nodejs + mongodb + koa2 write interface (3) add, delete, modify and query mongodb

    Time:2020-2-11

    1、 Open mongodb and wait to be connected Locate the mongodb installation location:For example, the path on my computer is C: / program files / mongodb / server / 3.6/bin Run mongod.exe, the default database interface is: 127.0.0.1:27017As shown in the figure below 2、 Run mongod.exe to operate the database 1. Create / delete / […]