mongodb relational database

number, manufacturer's name, component number, and manufacturer's address, but also manufacturer's name, the manufacturer's address, so there is a non-primary attribute transfer dependency on the main attribute, which does not conform to the third normal form requirementAfter modification:BC Paradigm: Based on the first paradigm, each non-trivial dependency must have a key code on the left side, and each determinant must contain a key code. Wikis: Any property, including non-primary and primary

Tags: type brackets unique order Chinese word breaker query files multiple columnsImprove query speed, facilitate sorting and grouping. (The process of sorting and grouping, if not indexed, results in temporary tables and filesort)Based on business logic, analyze the frequency and order of column queries, and build indexes and composite indexes.Primary key index (primary key),----> No index name is required because there is only one primary key indexUnique index (single key)---->unique Key Email

Label:Count: Count rows Select COUNT (*) from student Select count (age) from student/* will not count null values */ Sum: Returns the sum of the values in the column and automatically skips the null value (numeric +null=null) Select SUM (age) from student Avg: Returns the average of all values in the result set Select AVG (age) from student Max/min: Returns the maximum/small value in all values Select Max (age) from student GROUP BY: Data Group query Select Age,name,count (*) from the student

Tags: type SQL statement Delete Insert Number unique index explain not slow query1, positioning slow query-find out the execution slow SQL.2, suitable table structure, appropriate engine, index, partition table, SQL optimization (single machine Optimization).3, Multi-machine optimization--read/write separation (cluster), distributed.4, the cache scheme.Parsing slow query: Explain + SQL statement "using MySQL client"Indexes are at the expense of insertion, modification, and deletion (because addi

analysis and case of RDS availability of Aliyun relational database relational database service (relational DB service, RDS) is an open, reliable, flexible and scalable online database service. With multiple security measures and

Tags:date database updates nameget ways let Create end base SQLite--Embedded relational database 1. SQLite data type: typelessness (no type) 1, can save no matter what type of data to the table in the Random column 2. Supports common types such as: NULL, VARCHAR, TEXT, Integer, BLOB, CLOB, etc. 3, the only exception: integer primary key This field can only

We know that in a relational database there are four properties for a transaction: atomicity (atomicity): a transaction is executed as a whole, and the operations contained therein are either completely executed or not executed. Consistency (consistency): a transaction should ensure that the state of the database transitions from one consistent state

Label:Summary of performance optimization of relational database author: Liu Xiaojun Source: Blog Park Published: 2010-12-12 21:09 read: 2,763 recommendations: 1 original link [favorites]Absrtact: Today we are going to discuss the problem of performance optimization of relational database, usually we also better abide

First, the basic concept1 Relationship ModelTable : The concept of mathematical relationships is closely related, and the relational database is a collection of tables. A row in the table represents a link between a series of values.Properties : The first column of a table is called a property.domain : The value allowed by the property.A mathematical description.Relationship : A mathematical term that can r

Tags: core relationship arc tuple an independent display language controlChapter III relational database standard language SQL SQL Set data query, data manipulation, data definition and data control functions in one, the main features include: Integrated (unified language style for each part of the process) High degree of non-process Collection-oriented operation mode Provides multiple uses in the same synt

is the main code of the basic relationship s. If f corresponds to K, it is said that F is the outer code of R (foreign key). The basic relation R is referred to as the reference relation. The basic relationship S is the referenced relationship. The external code does not have to have the same name as the corresponding master code.(2) If the attribute (or attribute group) f is an outer code of the basic relationship R, it corresponds to the main code K of the basic relationship s (the basic rela

Tags:merge class relationships rowidoutchar Two kinds of hash join length row The left Join,inner join that is often heard in development, right join, and cross join are logical connections to the database, so how does the database implement the associated table at the bottom when the database is executing these connections? This is the physical connection. Mo

This is the Oracle Coherence 3.5 book, Chapter One: Achieving performance, Scalability, and availability Objectives, section II: Achieving Scalability, the database extends the part of the reading notes.Traditional relational databases are difficult to scale, usually vertically scaled, but scale horizontally only when they reach a certain level.The scale-out of the data