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1. Overall explanation: DML(data manipulation language): They are SELECT, UPDATE, INSERT, DELETE and, like their names, are the languages used to manipulate data in a databaseDDL(data definition language): There are more DDLs than DML s. The main commands are CREATE, ALTER, DROP, etc. DDL is mainly used to define or change the structure of tabl ...

In practical projects, it is often necessary to connect multiple databases, and different business needs often need to access different databases in the implementation process. jdbc.properties configuration file, configuring multiple dataSource s ##########################MySQL##################################### hibernate.dialect=org.hiberna ...

I. Isolation Level of Transactions Multiple transactions run simultaneously in the database. When they access the same data in the database, if the isolation mechanism is not adopted, some concurrency problems will occur. There are several concurrency problems in the database. (1) Reading "dirty" data refers to the fact that trans ...

Basics Create a database Determine whether the database exists before creating it if exists (select * from sysdatabases where name='databaseName') drop database databaseName go Create DATABASE database-name Delete the database drop database dbname Backup sql server Create a device for backing up data USE master EXEC sp_addumpdevi ...

1. Create EntityManager with annotations: /*unitName is used to select a specific PersistenceContext and the primary data source is selected by default, which passes through the.persistenceUnit("secondaryPersistenceUnit") when creating the bean s of the data source To create it by */on the object of EntityManagerFactoryBuilder @Pe ...

background Recently, due to job adjustments, we have been dealing with databases, which has increased many opportunities for close contact with JDBC. In fact, we are using Mybatis.Knowing it, knowing it, is what our engineers and children's shoes should pursue, to help you better understand this technology, and to be more comfortable when facin ...

Write at the beginning Recently, in the development of elastic search, there is a need to import the data of mysql specified tables into the index of elastic search. This requirement seems to be relatively easy. The general idea is to traverse every row of data in the table, convert it into json, and then submit it it to es through the api inte ...

The concept of cursor:A cursor is a memory workspace of SQL, defined as a variable by the system or user. The function of cursors is to temporarily store blocks of data extracted from databases. In some cases, data needs to be transferred from tables stored on disk to computer memory for processing, and finally the processing results are displa ...

Complete CRUD operation In the previous article, we had a brief idea of how Mybatis works and how it works. This time, we used Mybatis to complete the CRUD, reinforcing Mybatis development steps and some details Structure between Package and Class Increase Students configuration file <?xml version="1.0" encoding="UTF-8"?> < ...

Date examples: SELECT TO_DATE('2006-05-01 19:25:34', 'YYYY-MM-DD HH24:MI:SS') FROM DUAL SELECT TO_DATE('2006-05-01 19:25', 'YYYY-MM-DD HH24:MI') FROM DUAL SELECT TO_DATE('2006-05-01 19', 'YYYY-MM-DD HH24') FROM DUAL SELECT TO_DATE('2006-05-01', 'YYYY-MM-DD') FROM DUAL SELECT TO_DATE('2006-05', 'YYYY-MM') FROM DUAL SELECT TO_DATE('2006', 'YYY ...