Tag：Field name
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Time：2021-4-20
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 […]
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Time：2021-4-15
The company’s project has been basically developed based on MySQL. Suddenly, it needs to change the database. Originally, it thought that it was just to modify the configuration file. As a result, various errors and problems were reported. The main problems are as follows: 1. Key words Comment, start, etc. are keywords in Oracle and […]
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Time：2021-4-14
Focus on “Java back end technology stack” Reply to “interview” for full interview information MyBatisXML configuration and annotation configuration are provided. Today, let’s talk about how these two ways are realized. MyBatisIts real power lies in its statement mapping, which is its magic. Because of its extraordinary power, the XML file of mapper is relatively […]
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Time：2021-3-24
Focus on “Java back end technology stack” Reply to “interview” for full interview information At present, annotations are very popular. The code that used to be very long is now basically done with one annotation. So, where is itMybatisWhat are the notes in the text? MybatisThe annotations in are basically in theorg.apache.ibatis.annotationsUnder the table of […]
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Time：2021-3-16
The concept of index Index is essentially a data structure Type of index: From the perspective of data structure, it can be divided into three parts B+Tree index hashIndexes FULLTEXTIndexes R-TreeIndexes From the perspective of physical storage: Clustered index Nonclustered index From the logical point of view: primary key General index (single column index) Composite […]
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Time：2021-3-3
mobileWindow.js Because the company’s new project needs to achieve similar app operation in the mobile terminal, in order to quickly develop, of course, we hope to find a ready-made third-party class library to realize the relevant functions, but after a few days, we still haven’t found a particularly suitable one, so we started to write […]
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Time：2021-2-12
MySQL usage in Python 1、 Precautions To view the system version: Arch command to check whether the system is 64 bit or 32-bit Check kernel version with cat / etc / system release Pay attention to the version of MySQL Enterprise Edition: pay Community Edition: Free MariaDB Pay attention to avoid updating the version of […]
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Time：2021-2-11
Database: DDl:Create statementCreate, alter, drop, etc DML:Update data addition, deletion and modification insert,delete,update DCL:Define security levels and create users DQL:Used to query select,from,where Data type:Int / / integerDouble / / decimalDate / / dateVarchar() / / textTo create a library:Create database ‘database name’View database: show databases; Delete Library: drop database;Switch libraries:Use ‘Library name’; To create […]
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Time：2021-2-3
#Common constraints Create table name（ Field name, segment type, column level constraint, Field name field type, Table level constraints ) CREATE DATABASE students; #1、 Add constraints when creating tables #1. Add column level constraints USE students; DROP TABLE stuinfo; CREATE TABLE stuinfo( Id int primary key, # primary key Stuname varchar (20) not null unique, […]
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Time：2021-2-1
DDL: used to define RDB schema, external schema and internal schema. It has realized the definition, modification and deletion of basic tables, views and index files Create data table > create table structure > create table data data type […]
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Time：2021-1-31
Basic data retrieval: single table Complex data retrieval: multi table: join query, sub query (nested query), set operation Basic select statement: Select < search field > From < Table > Where < search criteria > Group by < classification > Having < search conditions > Order by < sort field > Control […]
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Time：2021-1-27
DQL: records in query table *Select * from table name; 1. Grammar: select Field list from Table name list where Condition list group by Group field having Conditions after grouping order by sort limit Paging limit 2. Basic query 1. Query of multiple fields Select field name 1, field name 2… From table name; *Note: […]
