Feel different CRUD with expression tree

Intro Recently, there is an idea that if you want to do something similar to ORM without writing sql statements, you can parse the expression tree, generate the sql statements to be executed, and finally execute the sql statements to return the corresponding results. Train of thought analysis The common sql statements basically have a certain m ...

Posted by rsmarsha on Fri, 06 Dec 2019 15:08:38 -0800

Analysis function sorting of oracle rookie learning

Ranking function 1. Row Ou number: returns a sequential sort, regardless of whether the values are equal or not2.rank: rows with equal values have the same order, and the order value then jumps3. Deny u rank: rows with equal values are ordered the same, and the sequence number is consecutive Experiment table create table chengji(sno number,km ...

Posted by dvidunis on Fri, 06 Dec 2019 09:13:44 -0800

Python MySQL extracts the first N data of each group in the table

In the process of large-scale data processing, sometimes it is necessary to take out a part of data by groups as a reference for the whole data. For example, there is a table [1], which can be divided into 200 groups by column [1]. Now we want to take 10 records from each group of these 200 groups as a representative. We can ope ...

Posted by techiefreak05 on Thu, 05 Dec 2019 03:10:24 -0800

AWS Athena analysis log

In AWS, Athena can be used to analyze the logs saved in S3. He can convert the logs into the format of database tables, so that they can be queried through sql statements. This function is similar to using logparser to analyze Exchange or IIS logs on a windows Server. Let's do a demonstration, record the management log through Cloudtrail, and ...

Posted by stubarny on Wed, 04 Dec 2019 09:10:56 -0800

Monitoring of druid data pool in spring boot project

Druid is the best database connection pool in Java language, which can provide powerful sql monitoring and extension functions. The industry compares Druid with HikariCP. Although the performance of HikariCP is higher than Druid, Druid includes many dimensions of statistical and analysis functions, so this is why everyone choose ...

Posted by nocturne on Wed, 04 Dec 2019 02:51:48 -0800

C ා dynamically create database 3 (MySQL)

The previous instructions use EF to dynamically create a database and a table. The database uses SQL SERVER2008, which is different when MYSQL is used I. add EntityFramework.dll, System.Data.Entity.dll, MySql.Data, MySql.Data.Entity.EF6 Note: Entity Framework 5.0.0 (it seems that the latest 6.X does not support mysql) 2. To add dll files, you c ...

Posted by nmpku on Wed, 04 Dec 2019 00:09:24 -0800

Technology sharing | thinking about MySQL show processlist with negative time

Author: Gao Peng At the end of the article, there is his book "in-depth understanding of MySQL master-slave principle 32", in-depth understanding of MySQL master-slave, GTID related technical knowledge. I. source of problems This is a question that a friend asked me. The question is as follows: what happens when the Worker thread s ...

Posted by Wildthrust on Tue, 03 Dec 2019 23:20:10 -0800

PHP dependency injection

How to call a method in a class: $class = new class();$class->fun() Dependency injection pattern is used to reduce the coupling between programs There are three modes of dependency injection: setter method injection Focus on setter method injection combined with ArrayAccess /** * Class Di * @property People */ class Di implements ArrayAc ...

Posted by Rebel7284 on Tue, 03 Dec 2019 23:09:05 -0800

MySQL restores single table data with full database backup data

When backing up the database, a full database backup is used, but for some reasons, the data of a table needs to be rolled back to the backup database. If the entire database needs to be rolled back, it will take time, because this table may only have tens of meters, but other tables may have tens of hundreds of G, so the tables that need to be ...

Posted by paulchen on Tue, 03 Dec 2019 11:20:06 -0800

Interpreter pattern of design pattern

introduce Role: It mainly includes the following roles: Expression: abstract expression. TerminalExpression: Terminator expression - is a symbolic expression. NonTerminalExpression: non terminator expression - numeric expression. Calculator: calculation class. Code Code scenario Interpreter to add and subtract. Specific code Expression /** * ...

Posted by dsdintn on Tue, 03 Dec 2019 07:54:13 -0800