Programmer Think

Execution order of SQL statement: FROM <left_table> ON <join_condition> <join_type> JOIN <right_table> WHERE <where_condition> GROUP BY <group_by_list> HAVING <having_condition> SELECT DISTINCT <select_list> ORDER BY <order_by_condition> LIMIT <limit_number> 1. LIMIT stateme ...

I. other precautions 1. For methods with static, we said that we need to use the method of "class name", but in fact, we can use the method of "reference" to access this method.   package com.bjpowernode.java_learning; ​ public class D43_ { public static void main(String[] args) { Test3.test3(); ...

I. When can't this be omitted? Let's give an example to illustrate class User2{ private int id; public int getId() { return id; } public void setId(int id) { this.id = id;//If it's written here id=id，Then according to the principle of proximity, the first id It's the formal parameter. The second one. id Als ...

In the first two lessons, we used a lot of regular expressions to match the city list, city and user information. In fact, in addition to regular expressions to match, we can also use goquery and xpath third-party library to match useful information. And I used more elegant regular expression matching. Let's talk about regular expressions. For ...

Data cleaning Data cleaning is a key step in data analysis, which directly affects the subsequent processing work. Does the data need to be modified? Is there anything to change? How should the data be adjusted for the next analysis and mining? It is an iterative process, and the actual project may need to perform these cleaning operations mo ...

[TOC] I. Overview of HDFS System Composition This is a distributed file system that is suitable for scenarios where multiple reads are written at one time. Contains the following roles: NameNode(nn): Store metadata of files, such as file name, file directory structure, file attributes and so on, as well as block list of each file and DataNode ...

1. Backup databaseBoth RMAN and expdp can be used.2. Backup Software Directory (node1/2) tar -czvf /u01/grid.tar.gz /u01/app/11.2.0/grid --exclude=/u01/app/11.2.0/grid/rdbms/audit/* tar -czvf /u01/database.tar.gz /u01/app/oracle/ --exclude=/u01/app/oracle/admin/orcl/adump/* 3. Backup OCR (node1/2) [grid@vastdata01 ~]$ cd $ORACLE_HOME/bin [g ...

Common terms of Kafka Broker: Kafka's server is an instance of Kafka. The Kafka cluster consists of one or more Brokers, which are responsible for receiving and processing client requests. Topic: Topic, a logical container for messages in Kafka. Each message published to Kafka has a corresponding logical container, which is often used to differ ...

Each write operation in Zookeeper maintains a transaction log dedicated to writing znode operations. Only the data changes confirmed by the transaction log will take effect throughout the cluster. 1,TxnLog TxnLog is a write transaction log interface, which mainly includes the following interfaces: rollLog: Log scroll to start a new log ap ...

Leader receives client requests by starting Leader Zoo Keeper Server. First, we look at the definition of its processing chain. From the source code, we can see that the sequence of the processing chain of LeaderZoo Keeper Server is as follows:   LeaderRequestProcessor: Leader call chain begins PrepRequest Processor: Write action prepar ...