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Usage specification It is strongly recommended that table names and field names be in lowercase or uppercase, and the default case sensitivity of NPC Jincang databaseCreating functions and stored procedures can be created using Oracle syntax, which is compatible with Oracle syntax. Avoid using keywords to create tables, views, functions, etc ...

preface This semester, we have a course of database principle and application, which is very difficult at the beginning, mainly because we didn't clarify the relationship between mathematical logic and database syntax in the process of SQL learning. Today, I would like to summarize my learning about SQL. I only briefly introduce the implem ...

Centos7 completely uninstalls MySQL & installs & starts Uninstall section 1. See what mysql has installed rpm -qa |grep -i mysql 2. Start the uninstallation, and execute the installed XXX in sequence: yum remove XXX 3. Check to see if the uninstall is complete rpm -qa |grep -i mysql 4. Find mysql related directory find / -na ...

PRIMARY KEY constraint Primary key is used to uniquely identify each record in a table. You can define one or more columns as primary keys. There can only be one primary key on a table;It is not recommended to update the primary key;No two rows on the primary key column have the same value (i.e. duplicate value), and NULL (NULL) is not allowed ...

An Apache Druid architecture 1. Coordinator Monitor historical processing, and be responsible for allocating segments to the specified service to ensure that historical data is self balanced 2. Overlord Monitor the MiddleManager to process and control data loading into the druid cluster; Responsible for the ingestion tasks assigned to the M ...

This paper mainly introduces the classification, viewing and modification of parameters in Dameng database. The main contents are shown in the figure: In Dameng database, its performance can also be maintained through a series of parameters. In the maintenance process, it is very important to master the maintenance of parameters. Parameter t ...

Spring Javaweb —Spring Spring closeout - transaction, web The key to integrating mybatis in Spring is the three objects: Datasource object, SqlSessionFactory object and dao object created by mappercannerconfig - all are completed in the configuration file. druid does not need driver information Spring transaction What is a tra ...

What are constraints? In order to ensure the integrity (accuracy and correctness) of the data in the table, some restrictions are added to the table. It is a basic rule of table design in database. Using constraints can make data more accurate and reduce redundant data (dirty data). Database integrity constraints are divided into the followin ...

mysql pxc high availability 1, pxc introduction PXC (Percona XtraDB Cluster) is an open source MySQL high availability solution. He integrates Percona Server and XtraBackup with the Galera library for synchronous multi master replication. The high availability solutions based on Galera mainly include MariaDB Galera Cluster and Percona Xtra ...

----Then day04 notes continue editing----- 3.2 external table: Description of external table: Because the external table loads the data of other hdfs paths into the table, the hive table will think that it does not completely monopolize the data. Therefore, when deleting the hive table, the data is still stored in hdfs and will not be delete ...