Tag:constraint condition

  • Introduction to database (IV) integrity

    Time:2021-11-16

    Integrity Similarities and differences between integrity and security Integrity: prevent data that does not conform to semantics in the database, that is, prevent incorrect data in the database. Guard against objects: non semantic and incorrect data.Security: protect the database from malicious damage and illegal access. Prevention object: illegal users and illegal operations. Entity integrity rules […]

  • How to convert external links to internal links?

    Time:2021-9-20

    Summary:If you can convert an outer join to an inner join, you can simplify the query optimization process. This article is shared from Huawei cloud community《Conversion of gaussdb (DWS) external connection to internal connection》, author: Wang Xiaojuan 8. In the process of query optimization, the connection order between internally connected tables can be exchanged at […]

  • L1L2 regularization

    Time:2021-3-31

    P-norm The definition of p-norm $\|\mathbf{x}\|_{p}:=\left(\sum_{i=1}^{n}\left|x_{i}\right|^{p}\right)^{1 / p}$ When p = 1, $\ | – boldsymbol {x}\|_ {1}:=\sum_ {i=1}^{n}\left|x_ {i}\right|$When p = 2, $\ | – boldsymbol {x}\|_ {2}:=\left(\sum_ {i=1}^{n}\left|x_ {i}\right|^{2}\right)^{\frac{1}{2}}$L1 norm is the sum of the absolute values of each element in the vector, L2 norm is the sum of the squares of each […]

  • Do you know what restful style is? Spring MVC takes us to implement it!

    Time:2021-2-1

    Restful style API is a kind of software architecture style, design style rather than standard, just provides a set of design principles and standardsconstraint condition. It is mainly used for client and server interaction software. The software designed based on this style can be more concise, more hierarchical and easier to implement caching and other […]

  • Data table operation of MySQL

    Time:2020-12-31

    Data table operation of MySQL Data table operation Each data table is equivalent to a file, which is divided into table structure and table record. Table structure: including storage engine, field, main foreign key type, constraint condition, character encoding, etc Table record: each row of data in a data table (excluding field rows) id name […]

  • Using database trigger to realize complex security check

    Time:2020-8-5

    1、 What is a trigger A database trigger is a stored PL / SQL statement associated with a table. Whenever a specific data operation statement (insert update delete) is issued on the specified table, Oracle automatically executes the statement sequence defined in the trigger. The application scenarios of triggers are as follows: Complex security checks […]

  • [Mr. Zhao Qiang] use database trigger to realize complex security check

    Time:2020-4-24

    1、 What is trigger Database trigger is a stored PL / SQL statement associated with a table. Whenever a specific data operation statement (insert update delete) is issued on the specified table, Oracle automatically executes the statement sequence defined in the trigger. The application scenario of the trigger is as follows: Complex security checks Confirmation […]

  • StarUML VI. StarUML rules and shortcuts

    Time:2020-4-11

    The content of this chapter can refer to the official website, without detailed description, practice out the truth! StarUML rules are mainly based on the constraints of model design https://docs.staruml.io/user-guide/validation-rules Shortcut keys https://docs.staruml.io/user-guide/keyboard-shortcuts   The next chapter begins to design UML common diagram model

  • In those years, we misunderstood rest together

    Time:2020-2-17

    Welcome to Tencent cloud + community to get more Tencent technology practice dry goods~ This article was published by sammyshen in cloud + community column In recent years, rest API is becoming more and more popular, especially with the concept of microservice widely accepted and applied, many web services use rest API. Rest is proposed […]

  • Table operations in MySQL

    Time:2020-1-8

    ————Resume content start———— Create database Create database database name Switch database Use database name Building tables: Create table table name( Field name 1, type, constraint Field name 2, type, constraint     …   ) Constraints: 1. Primary key constraint 1) Add the primary key after the field type when directly building the table 2) Add constraint constraint […]