Database Experiment 4: view and database security
[purpose and requirements of the experiment] 1. Understand the SQL view and its difference from the basic table; 2. Master the definition, query and update of SQL view; 3. Master the management methods of users and permissions in SQL Server; 4. Master the control function of SQL language; 5. De ...
Added by Roberto on Wed, 19 Jan 2022 14:05:39 +0200
Related sub query
-- Related sub query: sub queries cannot be run independently, and external queries must be run before sub queries
-- Advantages: simple and powerful
-- Disadvantages: difficult to understand
-- Query the employee with the highest salary in the Department
SELECT deptno,ename,max(sal) from emp GROUP BY deptno
-- The state ...
Added by stweaker on Wed, 19 Jan 2022 12:50:04 +0200
The original content of GreatSQL community cannot be used without authorization. Please contact Xiaobian and indicate the source for reprint.1. Problem descriptionOccasionally encountered gtid during MGR testing_ The executed transaction ID is discontinuous, but it does not affect the normal operation of the database. The phenomenon is as follo ...
Added by megavolt on Wed, 19 Jan 2022 12:39:58 +0200
When it comes to anomaly detection, the main challenge is that it is difficult to define anomalies. For example, how can we define and predict abnormal network intrusion, system defects and security fraud? If known exception data has been marked, we can choose from the various types of supervised machine learning models (see the link below fo ...
7: Database connection pool
7.1 necessity of JDBC database connection pool
When developing web programs based on database, the traditional mode basically follows the following steps:
Establish database connection in the main program (such as servlet and beans)Perform sql operationsDisconnect database Problems in the development of this m ...
Added by sell-traffic on Wed, 19 Jan 2022 03:46:08 +0200
This note is the learning content of Alibaba cloud Tianchi Longzhu plan SQL training camp. The link is: https://tianchi.aliyun.com/specials/promotion/aicampsql
1, Addition and subtraction of tables
1.1 what is set operation
A set represents "the sum of all kinds of things" in mathematics and a set of records in database Specific ...
Added by adt2007 on Tue, 18 Jan 2022 20:49:49 +0200
Characteristics of transactions
Atomicity: a transaction must be an atomic unit of work. All statements in a transaction must be done or none of them.Consistency: keep the data logically "reasonable". When A transfers to B, A must pay less and B must pay moreIsolation: if multiple transactions are executed concurrent ...
Added by Salsaboy on Tue, 18 Jan 2022 20:22:55 +0200
1. Premise environment
Install pypharm, and install the Scrapy frame in pypharm
2. Create a Scrapy project
Find Terminal in the lower left corner of pychart, as shown below: Click Terminal to enter the command line window, as shown below: In this window, execute the following command to create a Scrapy project
scrapy startproject ent ...
The original content of GreatSQL community cannot be used without authorization. Please contact Xiaobian and indicate the source for reprint.brief introductionPrometheus is an open-source combination of monitoring & Alarm & time series database. Usually, Kubernetes will cooperate with Prometheus for monitoring. Because the image of Prom ...
Added by infusionstudios on Mon, 17 Jan 2022 09:19:53 +0200
MySQL Learning Series
For some very performance-consuming statements, MySQL still tries its best to convert this bad statement into a more efficient form according to some rules. This process can also be called query rewriting.
The search condition of the query statement we write is essentially an expression. The ...
Added by KirstyBurgoine on Sun, 16 Jan 2022 09:06:36 +0200