And entity integrity is the integrity constraint that a relational model must satisfy, The purpose is to ensure data consistency. ġ0） Referential integrity : Referential integrity requires that nonexistent entities cannot be referenced in a relationship. An index is a structure that sorts the values of a column or columns in a database table. ĩ） Indexes : Use indexes to quickly access specific information in database tables.
Ĩ） Composite key : Composite key （ Composite key ） Use multiple columns as an index key, Generally used for Composite Index. ħ） Foreign keys : Foreign keys are used to associate two tables. You can use the primary key to query data. A data table can only contain one primary key. Ħ） Primary key : The primary key is unique. ĥ） redundancy : Store twice as much data, Redundancy reduces performance, But it improves the security of the data. Ĥ） That's ok : a line （= Tuples, Or record ） It's a set of related data, For example, a data subscribed by a user. ģ） Column : A column of ( data elements ) Contains the same type of data, For example, postal code data. A table in a database looks like a simple spreadsheet. Ģ） Data sheet : A table is a matrix of data. ġ） database : A database is a collection of related tables. Through combination analysis, New data can be generated. The priority of storing data in a database ： The so-called relational database, It's a database based on a relational model, With the help of set algebra and other mathematical concepts and methods to deal with the data in the database.
Ĥ） therefore, Now we use a relational database management system （RDBMS） To store and manage large amounts of data. ģ） We can also store data in files, But reading and writing data in files is relatively slow. Ģ） Each database has one or more different databases API Used to create, visit, management, Search and copy saved data. ġ） database （Database） It's organized according to the data structure 、 Warehouse for storing and managing data. MySQL Is the most popular relational database management system, stay WEB Application aspect MySQL It's the best RDBMS(Relational Database Management System： Relational database management system ) One of the application software.
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