SQL Server databases use views to process complex data query relationships and SQL data queries

Source: Internet
Author: User

SQL Server databases use views to process complex data query relationships and SQL data queries

The SQL Server database uses views to process complex data query relationships. This is what we will introduce in this article. This is what comes to mind: When we assist the educational administration system, one page I made is a query of the workload of a single teacher and the whole school teacher. This operation is designed into three tables in the database and one instructor information table in a different database, it is very difficult to use common SQL statements. Because of the video playing system I just started, there are relatively few tables in the database and there is no such complicated processing relationship involved, it was hard at first.

Later I thought that using a view could solve the complex relationship between multiple tables, but the other table is of different databases and whether the operation can still be performed. After testing, you can create a view relationship between two tables in different databases, so that the view is a virtual table. We put the tables in different databases to be queried or tables in the same database together, select the required field and create a new virtual table. Then, the view can be used as a new table for operations. This provides us with a lot of convenience.

A view is a continuous table that is inverted from one or more tables or views. Its structure and data are based on the query of the table.

Advantages of a view:

1. The view allows users to select specific data and specific tasks, while unnecessary or useless data can no longer be displayed in the view.

2. The view greatly simplifies database operations. You can perform table operations through view operations.

3. The view allows different users to view different or identical datasets in different ways, which is quite convenient.

4. in some cases, because the data volume in the table is too large, the table is often divided horizontally or vertically in the design of the table, but the structure change of the table has a negative impact on the application, the view can be used to reorganize data so that the external mode remains unchanged. The original application can reload data through the view.

5. view provides a simple and effective security mechanism.

View disadvantages:

If the view processes a large amount of data, it puts a lot of pressure on the SQL database, and the execution speed is relatively slow. Therefore, if you can use the stored procedure, prioritize the creation of Stored Procedures

View creation methods:

1. Create a view on the SQL server Management Platform

2. Use the create view command in the Transact-SQL statement to create a view

3. Create a view using the view template of the SQL sever Management Platform

Note the following when creating a view:

1. Only views can be created in the current database. A maximum of 1024 instances can be referenced in the view. The number of records in the view is determined by the number of records in its base table.

2. If the base table or view referenced by the view is deleted, the view cannot be used any more. You are advised to create a new base table or view.

3. If a column in the view is the same as a function, mathematical expression, constant, or column name from multiple tables, the column name must be defined.

4. You cannot create indexes on the graph any more. You cannot reference views in rules, defaults, or triggers.

5. when querying data through the view, SQL server checks to ensure that all database objects involved in the statement exist. Each database object is valid in the context of the statement, in addition, data modification statements cannot violate data integrity rules.

6. the view name must follow the rules of the identifier and be unique to each user. In addition, the name must not have any tables with the same name as the user. This is a created view, teacherInfo is added from another database.

The following is the data table "select * from QueryWorkInfoByFaculty" queried from the View"

This article describes how to use views to process complex data query relationships in SQL Server databases. I hope this article will help you gain some benefits!

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