database schema for messaging system

replaceSp_databases 4. sp_helptext Definition: displays the definition, default value, and unencrypted user-defined rules.Transact-SQLStored Procedures, user-definedTransact-SQLFunctions, triggers, calculation columns,CheckConstraints, views, or system objects (such as system stored procedures ). Note: It is very useful, especially for viewing the definition of a stored procedure. 5. sp_procop

converted to 3NF to maintain the decomposition of the function dependency.Algorithm 6.4 converted to 3NF decomposition with both non-destructive connectivity and function dependencies maintainedLossless connection decomposition of algorithm 6.5 (decomposition method) converted to BCNFAlgorithm 6.6 achieves 4NF of decomposition with lossless connectivityIf decomposition is required to have non-destructive connectivity, then the mode decomposition must be able to achieve 4NFIf the decomposition i

Database structure OptimizationHorizontal split of the tableThe common horizontal splitting methods are:1. Hash the customer_id, if you want to split into 5 tables use mod (customer_id,5) to remove 0-4 values2. Save the data to a different table for different Hashid.Challenge:1. Data query across partitioned tables 2. Statistics and Background report operation Operating system Configuration Optimiz

manages the database independently, as if each database is not a networked database. Each database is managed independently, called site autonomy. The advantages of site autonomy are as follows: The node of the system can reflect the logical organization of the company. L

Hibernate automatically creates a database table. Instead of creating a login user space, it creates a System space. Hibernate automatically creates a database table. Instead of creating a login user space, it creates a System space. Problem description: Hibernate automatically creates a

MariaDB 10.1.17 Released, MariaDB database management system is a branch of MySQL, mainly by the open source community in the maintenance, the use of GPL licensing MariaDB The purpose is fully compatible with MySQL, including the API and command line, so that it can easily become a substitute for MySQL.MariaDB the detailed introduction please login diligent study qkxue.net.Important Updates:XtraDB updated t

Overview This paper introduces the database design based on The three-paradigm of computer room charge system . Meets only the most basic functional requirements. Do not include additional information to save.RecallThe relationship pattern design has a Direct impact on data redundancy and data consistency. Thus, we have an evaluation indicator. That is the paradigm.First paradigm: Relational patterns R

A database engineer is to be tested this May. Mainly in order to take the title, in order to the omnipotent Beijing work residence permit, in order to give the baby to do medical card, the real battle has begun, refueling!No more say, start, First report the catalogue. Pure handmade! I hope that we will learn from each other more opinions.Chapter One, computer system knowledge1.1 Basic knowledge of computer

Sqlsessionfactory configuration, which requires specifying the MyBatis global profile, mapper.xml file location.XML version= "1.0" encoding= "UTF-8"?>Beansxmlns= "Http://www.springframework.org/schema/beans"Xmlns:xsi= "Http://www.w3.org/2001/XMLSchema-instance"Xmlns:context= "Http://www.springframework.org/schema/context"xsi:schemalocation= "Http://www.springframework.org/

, disk IO is small, so the disk does not need to be particularly high performance, concurrent requests are very frequent, more than the need for strong CPU processing capacity to handle Although the application and database interaction is very large, but each interaction data is small, the overall traffic will be larger, but generally the average gigabit NIC is enough.In many people's view, the fundamental determinant of performance is the quality of

use, difficult to maintain.Relational modelBased on rigorous data concepts.Correspondence Relationship:Relationship--tableTuples--RowsCode--An attribute groupDomain--a set of values that have the same data type. The value range of a property is derived from a domainComponent-a property value in a tupleRelationship pattern--a description of the relationship. such as the relationship name (attribute 1, property 2, ..., attribute N)Principle:Each component of a relationship must be a non-divided d

schema must be converted from a theoretical logical design to an actual physical design. The structure of the primary key and the foreign key is the crux of the design process. Once the designed database is used in production environments, it is difficult to modify these keys, so it is necessary and worthwhile to design the primary and foreign keys in the development phase. Primary key: The relational

Tags: database newsqlIntroducedGoogle's data system performance is very high requirements, MySQL such a system is difficult to satisfy, so Google Design F1 database, its goal is to have a high degree of scalability and high stability, in addition to the necessary SQL language support, F1 also provide ad hoc type query.

them by the last update time. Run the following statement: SELECT * from sys.objects where type in (' U ', ' V ', ' P ') Order by modify_dateThis statement identifies all the user tables, views, and stored procedures in the database and sorts them by time, so that you can see others recently added and modified those database objects. Sys.objects does not contain triggers, and triggers are in sys.triggers.

A data dictionary or system directory: A system database that describes the data information in a database and is a data or metadata data.Tuple-> row or record property-> the number of column or field tuples-> the number of cardinality attributes-> degreesA collection key-> a unique identifier for a-> table field-> A v

entities is the operator of the relationship's table and relationship;Second, the external view is also relational or close to the relationship;Thirdly, the internal mode is not the relationship, it is not the same as the copy of the relational table, even if the system is actually the same model (pointers, indexes, hash tables, etc.);System Architecture Diagram:　　Other important conceptsDatabase administr

* * The axiom system of data dependence is the theoretical basis of the model decomposition algorithm, Armstrong axiom system.* * Logic implication: To satisfy a set of function dependent F relationship pattern R(1) The relational schema r① reflexive law: if y belongs to x belongs to U, then x->y is implied by F;② Augmentation Law: If X->y is contained in F, and

connecting instructor and department to Dept_name, to get information from each mentor and his departmentCartesian product XThe Cartesian product outputs all the tuple pairs, such as the Cartesian product of the teacher and the department, indicating all possible correspondence.And ∪The parallel operation merges two tables with similar structures.For duplicate data in the result of the operation, some SQL languages strictly follow the mathematical definition of set operations to remove duplicat

join? Leave the left, right, and all unmatched rows separately.The equivalent expression for the left outer join is:(R?s) ∪ (R-πr (R?s)) x{(null,... NULL)}where {(null,... null)} is a schema after s-re) Extended operationGeneralized projection (generalized Projection)Generalized projections allow the operation of arithmetic and string processing at the same time as projection operations, such as:ΠID,NAME,SALARY*13 (instructor)Aggregation (aggregation