Programmer Think

1, Case analysis Table structure of query Get data from multiple tables: -- Wrong query method: query employees Tabular id and departments Name of the table SELECT employee_id, department_name FROM employees, departments; # 2889 records, there can't be so many, it's wrong SELECT * FROM employees; #107 SELECT 2889/107 FROM DUAL; # ...

1, First, consider a question: why does redis need a distributed solution with such high performance? 1. Achieve higher performance: for highly concurrent applications, the performance of a single machine will be affected. More redis servers are needed to share the pressure and achieve load balancing 2. Achieve high availability: prevent down ...

preface    in recent days, I have taken time to add several new functions to the code generator (it is expected to be released tonight). At present, it supports postgresql database, HikariCP connection pool and swagger2 (there is a link to the generator at the end of the article. Friends who like it can download it for free forever. ...

preface In CentOS, the default database is mariadb, so installing mysql is a little more difficult than before. Especially for novices, they just can't do it by looking at the documents. Very helpless, today I specially sorted out the detailed process of installing mysql in CentOS 7 for novices to learn. Experimental environment 1. Kernel ve ...

1, Foreword Let's look at an interesting case first The above sql queries two fields a and b, both of which are "Zhang San", and uses the length function to check that the length is 2. However, when you see the following sql output results, your first reaction is likely to be: "How is this possible?" In fact, as lik ...

Seata distributed transaction framework is widely used in the company, including four distributed transaction modes: AT, TCC, SAGA and XA. In fact, like TX-LCN framework, it can be said to be a variant of 2PC distributed transaction model, and its working principle is also similar. It is worth mentioning that the AT mode of Seata framework c ...

InfluxDB Incluxdb overview InfluxDB is a time series database built from scratch to handle high write and query loads. InfluxDB is designed to be used as a backup storage for any use case involving a large amount of timestamp data, including DevOps monitoring, application metrics, IOT sensor data and real-time analysis. What is time seri ...

Grain mall advanced level chapter Content directory: 1, ElasticSearch 1.1 introduction to elasticserch: Full text search is the most common requirement. Open source Elasticsearch is the first choice of full-text search engines. It can quickly store, search and analyze massive data. Wikipedia, Stack Overflow and Github all use it. The bo ...

1. Installation environment linux: centos 7.9 MySQL: 8.0.23 Installation directory: / opt/mysql (any directory can be used) Attach the download address of MySQL official website: https://dev.mysql.com/downloads/mysql/5.7.html#downloads , the interface after entering is as follows. Click the "Archives" tab to select different version ...

Preparation before learning: first create two tables for sentence experiment mysql -uroot -p show databases; create database plane; use plane; create table destination ( region char(20), place_name char(20)); insert into destination values('southwest','chengdu'); insert into destination values('north China','beijing'); insert into destinat ...