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Database Constraints Constraint type NOT NULL: indicates that a column cannot store a NULL value, that is, it must be assigned a value, otherwise an error is reported;UNIQUE: ensure that each row of a column must be a UNIQUE value;DEFAULT: Specifies the DEFAULT value when no value is assigned to the column;PRIMARY KEY: the combination of ...

Basic query Basic grammar select [distinct] * | {colunm1,colunm2,...} from table_name; characteristic 1,The query list can be fields, constants, expressions, functions, or multiple 2,The query result is a virtual table Basic query statement SELECT 1; #There are no clauses SELECT 9/2; #There are no clauses SELECT Identifies which co ...

catalogue 1. Overview 2. MySQL master-slave replication 3. Sharding JDBC implementation of read-write separation 4. MySQL sub database and table principle 5. Sharding JDBC implements sub database and sub table 1. Overview Shardingsphere Jdbc is positioned as a lightweight Java framework and provides additional services in the Jdbc laye ...

scene What are the files under Tag1, Tag2 and Tag3 in the many to many relationship table of a file and tag? id tag_id file_id 1 TAG_1 F1 2 TAG_2 F1 3 TAG_3 F1 4 TAG_1 F2 5 TAG_2 F2 6 TAG_3 F3 7 TAG_1 F3 For example, find the compliance TAG_1 and TAG_2 all documents below. Through observation, it can be found that F1 and F ...

Pre installation instructions Differences between CentOS6 and CentOS7 in MySQL usage: 1. Firewall: 6 yes iptables，7 yes firewalld 2. Command to start the service: 6 yes service，7 yes systemctl Installation of MySQL for Linux 4 major versions of MySQL MySQL Community Server The community version is open source, free to download, but doe ...

catalogue 1, Installing and configuring mysql module 1. Steps to operate mysql in a project 2. Install and configure mysql module (1) Install mysql module (2) Configure mysql module (3) Test whether the mysql module works normally 2, Using MySQL module to operate MySQL database 1. Query data 2. Insert data 3. Update data 4. Delete ...

I preface Mycat exposes services in the form of a Server, and its main configuration class is Server XML, this article mainly focuses on some small details, mainly including: Server. How to load XML Configuration and role in Server Flow of Server in connection request II Server.xml configuration 2 ...

Data filtering This chapter teaches how to combine WHERE clauses to create more powerful and advanced search conditions. We will also learn how to use the NOT and IN operators. Combine WHERE clause Last chapter( MySQL must know and know - Chapter 6 filtering data )All the WHERE clauses introduced in this article use a single condition when f ...

1.Error LogRecord the Error, Warning, Note and other information during MySQL operation. If there is a system Error or a record has a problem, you can view the Error log.MySQL's error log defaults to hostname Err is stored in the MySQL log directory and can be viewed through the following statementDuring default installation, the error log is u ...

Absrtact: the deep integration of cloud stack is the key to releasing the power of cloud database. Huawei cloud is in a leading position in achieving this goal, as proved by GaussDB(for MySQL). This article is shared from Huawei cloud community< Near data processing (NDP), crowning the performance improvement of GaussDB(for MySQL) >, auth ...