Tag：Relation
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Time：2021-9-21
1、 Interpretation typeThe type of the execution plan indicates the access data type. There are many access types. 1、systemThis means that only one row of data is returned in this step. If the execution object of this step is a driver table or main table, the driven table or sub query is accessed only once. […]
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Time：2021-9-18
1. What is the difference between #{} and ${}? Note: this question is for the interviewer to interview my colleagues. Answer: ${}It is a variable placeholder in the properties file. It can be used for tag property values and internal SQL. It belongs to static text replacement. For example, ${driver} will be statically replaced withcom.mysql.jdbc.Driver。 […]
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Time：2021-9-8
Explain features The results returned by explain are table granularity, and each table outputs one row. Here, it represents a table in a broad sense, which can be a sub query or a result after union. Not all explain queries do not execute. If the from clause contains subqueries, MySQL will actually execute subqueries to […]
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Time：2021-9-6
Execute query Once you have establisheddata modelAfter that, Django will automatically generate a set of database Abstract API, which allows you to add, delete, modify and query. This document explains how to use these APIs. For details on all model retrieval options, seeData model reference。 Throughout the documentation (and references), we will make extensive use […]
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Time：2021-9-4
Introduction: the topic shared by Flink meetup at Beijing station on May 22.This article summarizes the topic “practice of Flink in iqiyi advertising business” shared by Han Honggen, technical manager of iqiyi, at Flink meetup in Beijing station on May 22, including: Business scenarioBusiness practiceProblems and solutions in the use of FlinkFuture planning 1、 Business […]
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Time：2021-8-28
problem conductgit pushOperation error:fatal: The current branch master has no upstream branch. reason:The local branch is not associated with the branch of the remote warehouseadoptgit branchView local branches onlymaster adoptgit branch -aView remote branches, yesmasterandremotes/origin/masterTwo At this time, there are too many remote warehouses and many branches. By default,git pushIt is usually uploaded tooriginLowermasterOn the […]
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Time：2021-8-27
8.1 IO class IO library types and header files Header file type iostream Istream, wistream: read data from streamOstream, wostream: write data to streamIostream, wireless: write stream fstream Ifstream, wifstream: read data from fileOFSTREAM, wofstream: write data to a fileFsstream, wfstream: read and write files sstream Istringstream, wistringstream: read data from stringOstringstream, wostringstream: read data […]
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Time：2021-8-27
1、 Background When you encounter a requirement during development, you need to according to the device_ Code groups the data and obtains the latest piece of data in each group. 2、 Problems encountered 2.1 initial idea: first perform orderby on the data, and then perform groupby SQL statement: sql: SELECT * from y_device_events ORDER BY […]
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Time：2021-8-22
1、 Associated types When we read the rust program, the following code sometimes appears: trait Iterator { type Item; fn next(&mut self) -> Option<Self::Item>; } Here is the comment of the above code: iterator trait has an association typeItem。ItemIs a placeholder type, and the next method will returnOption<Self::Item>Value of type. thistraitThe implementer of will specifyItemSpecific […]
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Time：2021-8-20
1、 ORM programming idea 1.1 active record design mode Active RecordIt’s a kind ofData access design pattern, it can help you implement data objectsObjectMapping to a relational database. applicationActive RecordThe instance object of each class uniquely corresponds to a row (one-to-one relationship) of a database table. You only need to inherit oneabstract Active RecordClass can […]
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Time：2021-8-20
Pay attention to the warehouse and get updates in time:iOS-Source-Code-Analyze Follow: Draveness · Github This article is rightFBRetainCycleDetectorAnalysis of the association object mechanism implemented in; Because of the need of tracking, fbretaincycledetector re implements the associated object. This paper mainly analyzes the method of realizing the associated object. The main classes involved in this article […]
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Time：2021-8-20
Original link:http://tecdat.cn/?p=22732 Association rule mining is an unsupervised learning method, which mines rules from transaction data. It helps to identify relationships and items in the dataset. In this article, I will explain how to extract association rules in R.The association rule model is applicable to transaction data. An example of transaction data can be a […]
