• SQLITE_ERROR – table XX has no column named currency


    During the sap cloud application programming exercise, we encountered the following error message:SQLITE_ERROR: table sap_capire_bookshop_books has no column named currency In my schema definition, there is a field called current in books entity, but its data type is currency, which comes from @ SAP / CdS / common, not build in data type, such as […]

  • Object oriented programming (OOP) guide in Perl


    Object oriented programming: as the name suggests, object-oriented programming or OOP refers to the language that uses objects in programming. Object oriented programming aims at realizing real-world entities such as inheritance, hiding and polymorphism in programming. The main purpose of OOP is to bind data to the function that operates on it, so that no […]

  • MySQL optimization 3 (optimization rules)


    When you look at the following content, make sure you can use explain to analyze SQL! Single index table optimization case: Question:For example, we want to query the first record sorted by user name with password = 666 and age > 30. After analysis, we will find that the SQL internal optimizer has carried out […]

  • Improve productivity, the most complete mybatis plus explanation!


    Hello everyone, I’m a piece of cake, a piece of cake eager to be Cai Bucai in the Internet industry. Soft or hard, praise is soft, white whoring is just!Ghost ~ remember to give me a third company after watching it! This article mainly introducesUse of mybatisplus If necessary, please refer to If it helps, […]

  • Mongodb join table query


    Database table Table 1: data record table var mongoose = require(‘mongoose’), Schema = mongoose.Schema; var DocViewSchema = new Schema({ RealName: string, // real name User name: string, // OA account Count: number, // document statistics Docname: string, // document project name DOCTYPE: string, // document item type Orgpath: string, // the organization path of the […]

  • A thousand lines of MySQL commands


    basic operation `/*Windows services*/ –Start MySQL net start mysql –Create windows service sc create mysql binPath= mysqld_ bin_ Path (Note: there is a space between the equal sign and the value) /*Connecting and disconnecting servers*/ MySQL – H address – P port – U user name – P password Show processlist — shows which threads […]

  • Django uses or conditional queries and various query keywords


    Django uses or condition query: from django.db.models import Q User.objects.filter(Q(state=0) | Q(state=1)) Django query keywords: __ Exact equals like ‘AAA’__ Iexact is exactly the same as ignore case like ‘AAA’__ Contains contains like% AAA%__ Icontains contains ignore case like ‘% AAA%’, but for SQLite, the effect of contains is equivalent to icontains.__ GT greater than__ […]

  • Independent innovation of blockchain technology should pay more attention to the exploration of blockchain application


    Blockchain has appeared for nearly a decade. From the initial concept to the implementation of some blockchain application development, blockchain has never been recognized by people to now be valued by the field, and has experienced different market changes. Last week, the application of blockchain technology in China set off a discussion boom. The government […]

  • Mongodb database — learning records (2)


    3. Mongodb add delete modify query operation 3.1 creating a collection There are two steps to create a set: one is to set rules for the set, the other is to create a set and create a set mongoose.Schema Constructor to create the collection. //Set set rules const courseSchema = new mongoose.Schema({ name: String, author: […]

  • What does go ORM do?


    Fat Sir: next, I’ll give you a pie Chief: come on!!A note from ORM What is ORM? Why ⽤ ORM? What is ORM, or object relational mapping? Its purpose is to make a mapping between relational databases and objects, In this way, we don’t need to deal with complex SQL statements when we operate the […]

  • An update statement from a colleague made me miserable enough


    Source: ju.outofmemory.cn/entry/336774 Recently, several development students have asked me on the nail, such as the following figure: The problem can be summed up as follows:Update a record in MySQL. The syntax is correct, but the record has not been updated When I first encountered this problem, I got this statement and executed it directly in […]

  • MySQL Optimization: Performance Analysis of like and =


    introduction Most of the people who have used the database know the similarities and differences between the functions of like and = signs 1, difference: like can be used as fuzzy query, but ‘=’ does not support this function. For example, query the data whose first letter of field ID in info table is 1 […]