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Materialized view plays an important role in data analysis of database( Related concept record link )However, MySQL and other databases only have ordinary views and do not implement materialized views. We can manually implement similar functions according to the idea of materialized view, that is, use an entity table to store frequently accesse ...

In the project, when a statistical demand is encountered, statistics are made from a table according to conditions, and count(distinct case when) is used to solve this problem. count() function In statistics, count appears most frequently Simplest usage select count(*) from table where .... select count(distinct column_name) from table whe ...

1, SpringBoot advanced usage 1. Lombok plugin 1.1) Maven coordinate query website: https://mvnrepository.com/ You can now find information about the maven package 1.2) add jar package file <!--add to lombok rely on--> <dependency> <groupId>org.projectlombok</groupId> <artifactId&g ...

prefaceIn this paper, we will introduce several methods related to iterators in Rust language from a simple algorithm problem to help you understand chars, all, try_ fold,enumerate,try_ for_ each,char_ Use of indices. ​The title is as followsWe define that capitalized words are correct when:quoteAll letters are capitalized, such as "USA&qu ...

Click "Lifetime", Focus, Top Public Number Daily Technical Dry, First Time Delivery! Relational structured storage has some drawbacks because it requires all columns and their corresponding types to be predefined. However, the business may need to expand the descriptive capabilities of individual columns as it evolves, and w ...

1, What is a Session Session is an interface (HttpSession).A Session is a Session. It is a technology used to maintain an association between a client and a server.Each client has its own Session.In the Session session, we often use it to save the information after the user logs in. 2, How to create a Session and get (id number, new or not) H ...

Redis (Remote Dictionary Server), that is, the remote dictionary service, is an open source service using ANSI C language Write, support network, memory based and persistent log type, key value database , and provides API s in multiple languages Redis's role: In memory storage, persistence (RDB and AOF)Efficient and can be used for cachin ...

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 ...

1. Defects of sentinel mode In sentinel mode, there is still only one Master node. Sentinel mode does not relieve write pressure when concurrent write requests are large. 2. Redis cluster concept (1) A distributed network service cluster composed of multiple Redis servers; (2) There are multiple Master master nodes in the cluster, and each ...