Programmer Think

Alicloud (CentOS7.4) installs MySQL and connects MySQL locally and remotely Install MySQL using yum Step 1: check whether mysql exists on this machine rpm -qa | grep mysql yum info mysql-community-server Step 2: copy the download address of Yum community mysql on the official mysql website https://dev.mysql.com/downloads/ https://dev ...

1. Exits statement When MySQL treats the EXISTS clause, it still adopts the execution method of nested subquery. As shown in the following SQL statement: SELECT * FROM my_neighbor n LEFT JOIN my_neighbor_apply sra ON n.id = sra.neighbor_id AND sra.user_id = 'xxx' WHERE n.topic_status < 4 ...

JDBC The JDBC interfaces provided with the Java standard library actually define a group of interfaces, and a specific jdbc driver is actually a class that implements these interfaces In Java code, if you want to access MySQL, you must write code to operate the JDBC interface. Note that the JDBC interface comes with the Java standard library, ...

1 SQL overview 1.1 what is SQL SQL (Structured Query Language) is a "structured query language", which is an operation language for relational databases. It can be applied to all relational databases, such as MySQL, Oracle, SQL Server, etc. SQL standards (ANSI/ISO) include: 1. SQL-92: SQL language standard issued in 1992; 2. SQ ...

Start and stop of service When GBase 8a is installed, GBase.com The server service needs to be started manually. After that, whenever the machine is powered on and restarted, GBase All server services need to be started manually. If the user needs to manually start and stop the GBase service during use, the user who installed GBase 8A should b ...

1, View 1. Concept View is to wrap a more complex query statement in the view to simplify the statement. Views are stored in the database and can be reused. Data is not stored in the view. The data of the view exists in the base table of the view and changes based on the change of the table data. 2. Why use views? In order to facilitate ...

preface I'm going to open a new series, which is a new field I haven't touched much before, called performance tuning. When I read the word "performance tuning" when I was brushing my blog, I was stunned and felt that time had stagnated. I found that I didn't know the performance level of the project code I wrote. Even if it ...

CREATE DATABASE IF NOT EXISTS cms DEFAULT CHARACTER SET utf8; USE cms; -- Administrator table cms_admin CREATE TABLE cms_admin( id TINYINT UNSIGNED AUTO_INCREMENT KEY, username VARCHAR(20) NOT NULL UNIQUE, password CHAR(32) NOT NULL, email VARCHAR(50) NOT NULL DEFAULT 'admin@qq.com', role ENUM('General administrator','Super administrator') ...

1. General Trigger is a special stored procedure. Like stored procedures, triggers are SQL fragments that can complete specific functions and are stored on the database server. However, triggers do not need to be called. When DML operations are performed on the data in the database table, the execution of this SQL fragment is automatically tri ...

The difference between Oracle and Mysql 1, Main differences 1. Software specification: Oracle is a large database, which occupies a lot of memory;Mysql is a lightweight database, which is lightweight and occupies less memory; ps: I pulled the image of the two with docker. mysql is 545M in size, while oracle11g requires 6.85G 2. Expenses: ...