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Distributed cache - detailed explanation of Redis basic functions 1. Preface After several years of development, the concept of cache should be familiar. Common cache components include redis, mongodb and memcached. This article briefly introduces the common usage scenarios of redis and the use of basic APIs. redis is a database based on key ...

MySQL command integration (II) De duplication of query results select distinct ... // Add the distinct keyword after select be careful The distinct keyword can only appear first of all fields join query classification According to grammar SQL92SQL99 According to the connection mode of the table Internal connection: equivalent conn ...

1, Initial experience of MySQL database Basic concepts of databaseDevelopment of databaseIntroduction to mainstream databaseMySQL installation methodOperating MySQL 1. Basic concept of database Data A symbolic record describing somethingIncluding numbers, words, graphics, images, sounds, archives, etcIt is stored in a unified format in ...

Definition: exceptions in Exception except RuntimeException and its subclasses. Features: the Java compiler will check it. If such an exception occurs in the program, For example, ClassNotFoundException (the specified class exception is not found) and IOException (IO stream exception), either declare and throw it through throws or catch it thr ...

Composition of database SQL Server database consists of a set of operating system files, which are divided into two categories: data files and log files. 1. Data file: contains data and objects, such as tables, indexes, stored procedures and views. Data file typecharacteristicMaster data fileIt contains database startup information and ...

Query statement (DQL) 1.5. 1 simple query statement Syntax format: select field name 1, field name 2, field name 3 From table name; Tips: Any sql statement that ends with a semicolon sql statements are not case sensitive mysql> select Empno,ENamE from -> emp; +-------+--------+ | Empno | ENamE | +-------+--------+ | 7369 ...

13.1 introduction In the process of program development, we often need a lot of program debugging and troubleshooting. In the beginning stage, we often use South and debug to debug the program. The output information of the console is not detailed enough most of the time, so the log factory was born. We can more easily view the background log ...

1, Slow query log learning 1. What is slow query log? The slow query log of My SQL is a kind of log record provided by MySQL. It is used to record the statements whose response time exceeds the threshold in MySQL, specifically the statements whose running time exceeds long_query_time value, it will be recorded in the slow query log.long_ quer ...

In development, we often encounter some requirements for delayed tasks. for example If the order has not been paid for 30 minutes, it will be automatically cancelled Send a text message to the user 60 seconds after the order is generated For the above tasks, we give a professional name to describe, that is, delayed tasks. Then a question aris ...

catalogue 1. Primary key constraint Format 1: set when writing fields when creating a table Format 2: create a table in. Declare the primary key constraint after the column Format 3: after creating a table, modify the table structure and declare the columns as primary keys 2 . Unique constraint Format 1: set when writing fields when creat ...