Example Of Foreign Key Examples Computer Science Essay

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A key is a set of columns, and can be used to identify or access a particular row or rows. The key is to determine the description of a table, index, or referential constraints. The same columns, which can be a plurality keys.A only part of the key is a key constraint, therefore, its value is equal. The only key column can not contain NULL values. For example, the employee number field can be defined as a unique key, because each value in the column, to determine if there is only one employee. No two employees can have the same number of employees.Perform a mechanism called a unique index. Columns in the unique index of one or more tables each value identifies determine the ordered collection of a unique line features. Unique index can contain a NULL value. Define the primary key is a key on the table, but first an important key. The following table can have only one primary key. The primary key of the primary index is automatically created. Database management, and efficient access to the rows in the table, and allows the database manager to perform the primary key unique key indicators. (You can also query processing in non-primary key columns, efficient access to data definition index) If the table is not a "natural" unique key, if the arrival order method is used to distinguish the unique line, you can use the timestamp key is to help the primary key that uniquely identifies each row in a table, the table. It can use as a foreign key of the other table.

Example, the Customer table CustomerID condition (ordinarily automatically Ordering integer generated sequence) to uniquely identifies each row in the table. This value will appear in the "orders" table foreign key commands confederative customers. Although the unique single primary key value is the best, they can also be a "compound" key, i.e., in each row of the two or more values??. For example, a table, which includes the airline's flight data to uniquely identify the bank may use a composite key flight number and destination.

In relational database design, a unique key or primary key to uniquely identify each row is a candidate key. Unique key or primary key by one or a group of columns. No two different rows in the table have the same value (or a combination of the values??) can be in these columns. Depending on its design, a table can have any number of unique keys but at most one primary key. No primary key of the database will not run properly.

Example of Foreign key examples

SalesOrderHeader.SalesPersonID is a foreign key. A foreign key, also known as the foreign key is a key in the database table, refers to a specific key, usually the primary key in another table is being used in the table. Can be targeted multiple primary key foreign key from the other table. However, the primary key is not necessarily the any foreign key goal.It can change the primary key in the table specific user needs change. For example, people in a small town may be uniquely identifies their driver's license number in an application, but in another case, it may be more convenient to them based on their phone number. Be changed when a group associated foreign key primary key in a table, if there are any changes frequently as a result.The generic name of the foreign key automatically connected together. People are often confused about MySQL foreign key thing in all the MyISAM table engine does not support foreign keys. , MySQL will quietly ignore, rather than an error message when adding a MyISAM table foreign key foreign key definition. Foreign key support for InnoDB table engine, so you should make sure that all you want to add foreign key table is InnoDB table types.

Questions 2

Explain the main characteristics and the advantages of the following terms

Relational Database

Object Oriented Database

Object Relational Database

Relational Database

One of the most popular relational database to store large amounts of data. In a relational database, data organization, to make it easier for users to understand the data. It allows information to the packet or type of comparison can be easily performed, such as a year or name. Function relational database to provide a wide range of functions, create advanced data processing technology. They support the relational algebra and set operations. This includes the operation selection, join and split. These operations can only use a relational database. The query uses this data processing is possible, general in the Structured Query Language (SQL), manage data, and provide users with the information they are looking for. A relational database relationship or a collection of tables. The rows of the table in the relational database is called a tuple of a table for each column are called attributes. Tuples into a group having the same properties according to the definition of the relationship.

Operation relationship, you can select, project, and join. JOIN operation binding relationship, for data retrieval query and operation of the project identifier property. Similar to the other database models, relational database support insert, delete, and update operations. Advantages of Relational Database is Data Structure the table format is simple and easy for database users to understand and use. Multi-User Access. RDBMSs allow multiple database users to access a database simultaneously. Network Access. RDBMSs provide access to the database through a server that listens for requests on a network, and allows database clients to connect use the database. Speed. RDBMS make the slower speed. RDBMSs to perform more than fast enough for most applications and data sets.

Object Oriented Database

An Object database (also object-oriented database management system) is a database management system, in the system, the information that the form of the object in the object-oriented programming. Is different from a relational database, object database, belonging to a wider range of database management systems together. Advantages of Object Oriented Database is Designer can specify the structure of objects by using methods. Makes better interaction with object-oriented languages such as Java and C++ and user can predefine methods that are going to be used.C:\Users\System Manager\Desktop\320px-Object-Oriented_Model.svg.png

Object Relational Database

Combine relational databases and object-oriented programming features of object-relational database. This means that, when the development of these databases, you can include the methods and data types.This increases your ability to sort through and find files faster speed in these databases. Through these type of data file, you can filter them through a database. You can also retrieve files share the same characteristics. Advantages of Object Relational Database is Facilitate implementation of the domain model. This is one of the reasons, to replace all others. In short, the use of this model means that your entity model based on real business concepts, rather than based on the structure of your database. Provide this functionality through the the mapping ORM tool between the business logic models and physical storage model.C:\Users\System Manager\Desktop\article-new-intro-modal_ehow_images_a05_b7_m5_advantages-object-relational-database-800x800.jpg