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join query MySQL connection query usually combines the record rows from two or more tables to splice data based on the common fields between these tables. First, determine a main table as the result set, and then selectively connect the rows of other tables to the selected main table result set. Connection queries that are frequently used ...

1, Database function 1. Mathematical function The records stored in the database often need a series of arithmetic operations, so MySQL supports many mathematical functions. Common mathematical functions Mathematical functiondescribeabs (x)Returns the absolute value of x; The absolute value is always positive, and the absolute value o ...

introduction With the rapid development of office automation and e-commerce, enterprises rely more and more on information system. Database, as the core of information system, plays an important role. Database backup is an important means to recover important data in time and prevent data loss in case of data loss. A reasonable database ...

Database connection pool Concept: in fact, it is a container (Collection) for storing database connections After the system is initialized, the container is created, and some connection objects will be applied in the container. When the user accesses the database, the connection objects will be obtained from the container. After the user ...

1, Introduction to mysql lock Lock source When there are concurrent operations, a mechanism is necessary to ensure the integrity and consistency of data. Lock is the realization of this technology. Lock type According to the concept, it is divided into pessimistic lock and optimistic lock According to particle size: Table lock, page ...

MySql database is a relational database MySQL database is not case sensitive Some grammars in this article, such as goudan, dachui and Cuihua, are not fixed grammars and can be named arbitrarily data typeintegerint(m) m indicates the lengthLong integerbigint(m)Floating point numberdouble(m,d) m represents the total length d and the decimal po ...

Oracle advanced query Advanced query is widely used in database development. This paper introduces Oracle advanced query from three aspects: grouping query, multi table query and sub query. Grouping query Grouping query is to group according to certain rules. After grouping, data will be aggregated, and aggregation function is required. Howe ...

DB4AI tries to help users get rid of tedious data handling, export and management by implanting AI computing power into the database. It sounds reasonable to use the database to store massive data, but in the face of a traditional database, users as algorithm engineers or AI beginners have to export the data of the data set and then import it i ...

JDBC and DBUtils tools What is JDBC? In Web development, it is inevitable to use database to store and manage data. In order to provide support for database access in Java language, SUN company provided a set of standard Java class library for database access, namely JDBC, in 1996 The full name of JDBC is Java Database Connectivity, which is ...

  catalogue 1. redis installation 2.Redis's single thread and high performance 3. Five core data structures are most commonly used in redis Internet 3.1 common string operations 3.2 string common scenarios 3.2.1 single value cache 3.2.2 object cache 3.2.3 distributed lock 3.2.4 counter 3.2.5 counter 3.2.6 Web Cluster session shari ...