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​ Database benefits 1.Persistent data to local 2.It can realize structured query and facilitate management Database related concepts 1,DB: Database, a container that holds a set of organized data 2,DBMS: Database management system, also known as database software (product), is used for management DB Data in 3,SQL:Structured query langu ...

1. Why master slave copy In a system with complex business, there is a scenario in which an sql statement needs to lock the table, resulting in the temporary inability to use the read service, which will greatly affect the running business. Use master-slave replication, and let the master database be responsible for writing and the slave datab ...

This is a record of the whole back-end development of a real landing project, recording the process from 0 to 1 of the projects I saw and participated in. catalogue 1, Project overview 2, Project development process level 3, Development technology level 4, Reading notes during the project 5, Summary 1, Project overview Let's talk about ...

Welcome to the MySQL technical articles shared by the great SQL community. If you have any questions or want to learn, you can leave a message in the comment area below. After seeing it, you will answer it The original content of GreatSQL community cannot be used without authorization. Please contact Xiaobian and indicate the source for repr ...

Environmental preparation kettle mysql database Python environment requirement Use the preprocessing tool (kettle) to clean up the provided text data and import it into the database;Analyze and count the cleaned data, count the average expenditure of users in each city on traffic and voice, draw a chart with Python, and save the results;Coun ...

Access Remote Sources with SAP HANA Database Explorer Remote sources are connections to other databases. Virtual tables use remote sources to create local tables that point to data stored in another database. Federated queries use virtual and non virtual tables. To illustrate these concepts, a table will be created in the remote database cont ...

Welcome to the MySQL technical articles shared by the great SQL community. If you have any questions or want to learn, you can leave a message in the comment area below. After seeing it, you will answer itThe original content of GreatSQL community cannot be used without authorization. Please contact Xiaobian and indicate the source for reprint. ...

resultMap mapping What is resultMap? Simply put, it is a Map like structure that maps the fields in the database to the attribute fields in the JavaBean, so that one-to-one mapping can be achieved.How to write the above example using resultMap? As follows: <!--Create a resultMap mapping--> <resultMap id="patResultMap" type="com.xxx. ...

`public class AtomicInteger extends Number implements java.io.Serializable { // setup to use Unsafe.compareAndSwapInt for updates private static final Unsafe unsafe = Unsafe.getUnsafe(); private static final long valueOffset; static { try { // Calculates the offset of the variable value in the clas ...

join query Meaning: it is also called multi table query. When the query fields come from multiple tables, the join query will be used Cartesian product phenomenon: Table 1 has m Row, table 2 has n Line, result=m*n that 's ok Cause: there is no valid connection condition How to avoid: adding valid connection conditions As follows: #Without ...