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In daily work, we often need to develop reports or count the percentage and total of some data. At this time, the following functions can solve the problem quickly. They have fewer sql statements and better performance. The figure below shows the results of our statistics.                                                                     Co ...

[toc] Article content picture upload failed, welcome to read, eBook in white. Preface Statement: Refer to the source Internet, any disputes can be left a message.Standing on the shoulders of the forefathers, we can see farther.This tutorial is all hands-on, dedicated to the most practical tutorials, does not require any rewards, and only wishe ...

In the previous several articles, we introduced abp vNext microservice framework, development environment construction and access to the front-end framework of vue element admin respectively. After the basic functions of user role management are implemented in vue element admin, we can start business development. This article will introduce how ...

Zero. Preparations <dependencies> <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java --> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>8.0.20</version> </dependency> <!-- https://mvnre ...

Table Join Query 1. What is a multi-table query Preparing data # Create Department Table create table dept( id int primary key auto_increment, name varchar(20) ) insert into dept (name) values ('Development Department'),('Marketing Department'),('Finance Department'); # Create employee table create table emp ( id int primary key auto_in ...

mybatis cache Mybatis caches have a first-level cache and a second-level cache. Why do mybatis use two caching mechanisms?Let's move on to today's topic with questions. mybatis Level 1 Cache When the mybatis cache executes the same SQL and the same parameters, it does not make repeated calls to the ...

In the process of performance test, we often encounter the performance bottleneck of Mysql. For the database, the so-called performance bottleneck is nothing more than slow SQL, high CPU, high IO, and high memory. The first three examples are used for performance analysis. Finally, the high memory is ...

Lifecycle requested in Django 1. Overview First, we know that all data transferred in HTTP requests and server responses is strings. In Django, when we visit a url, we enter the corresponding html page through route matching. Django's request life cycle is what happens behind the scenes when a user enters a url into the browser and the user see ...

There are many ways to connect hive and impala in python, including pyhive,impyla,pyspark,ibis, etc. in this article, we will introduce how to use these packages to connect hive or impala, and how to pass kerberos authentication. Kerberos If the cluster does not enable kerberos authentication, the ...

Create Streaming DataFrame and Streaming Datasets Streaming DataFrames are available through SparkSession.readStream() The returned DataStreamReader interface (Scala / Java / Python document) is created. Input Sources Common built-in Sources File source: Reads files from a specified directory as st ...