Programmer Think

🎈 Write in front   🙋‍♂️ Hello everyone, I'm super dream. We all know that we have to deal with the database almost every day, whether in study or daily work. In order to better operate the database, our SQL knowledge reserve is essential. If you want to master SQL well, you must practice and study every day. Next, Xiaomeng will le ...

Alicloud (CentOS7.4) installs MySQL and connects MySQL locally and remotely Install MySQL using yum Step 1: check whether mysql exists on this machine rpm -qa | grep mysql yum info mysql-community-server Step 2: copy the download address of Yum community mysql on the official mysql website https://dev.mysql.com/downloads/ https://dev ...

1. Exits statement When MySQL treats the EXISTS clause, it still adopts the execution method of nested subquery. As shown in the following SQL statement: SELECT * FROM my_neighbor n LEFT JOIN my_neighbor_apply sra ON n.id = sra.neighbor_id AND sra.user_id = 'xxx' WHERE n.topic_status < 4 ...

1, SSL introduction SSL (Secure Socket Layer) uses data encryption, authentication and message integrity verification mechanisms to provide security assurance for application layer protocols based on reliable connections such as TCP. The functions provided by SSL protocol mainly include: 1. Confidentiality of data transmission: use symmetric ...

1, select statement Overall form of Select statement: select col1, col2... // Column name to find from table_name // Which table do you want to search where condition // Set search criteria group by col... // Set grouping having condtion // Set grouping conditions order by col... // Set sort The following examples illustrate the specific u ...

See the official website for details: Roll up and query && Materialized view Rollup and query In Doris, Rollup, as a polymer view, can play two roles in query: IndexesAggregate data (only for aggregate model, i.e. aggregate key) However, in order to hit the Rollup, certain conditions must be met, and whether the Rollup can be hit ca ...

1. Hype-V virtual machine installation openEuler There are many virtual machine platforms, such as vmware, Hype-V, VirtualBox, etc. Considering the compatibility with wsl2, Hype-V is selected here to install the x86 architecture openEuler Turn on the hype-v virtual machine Download the x86 architecture openEuler image Open the openEuler of ...

JDBC The JDBC interfaces provided with the Java standard library actually define a group of interfaces, and a specific jdbc driver is actually a class that implements these interfaces In Java code, if you want to access MySQL, you must write code to operate the JDBC interface. Note that the JDBC interface comes with the Java standard library, ...

1, Project introduction Title Requirements: Functional requirements: 1. Add student functions: name, student number, gender, date of birth. (Note: the student number is automatically generated and must be unique) 2. Add student achievement function: suppose everyone has chosen Chinese, mathematics and English. However, when inputting grades ...

1 SQL overview 1.1 what is SQL SQL (Structured Query Language) is a "structured query language", which is an operation language for relational databases. It can be applied to all relational databases, such as MySQL, Oracle, SQL Server, etc. SQL standards (ANSI/ISO) include: 1. SQL-92: SQL language standard issued in 1992; 2. SQ ...