What are MySQL views used for?

When should SQL views be used?

Views are virtual tables that can be a great way to optimize your database experience. Not only are views good for defining a table without using extra storage, but they also accelerate data analysis and can provide your data extra security.

What is the main purpose of views in SQL?

Views are generally used to focus, simplify, and customize the perception each user has of the database. Views can be used as security mechanisms by letting users access data through the view, without granting the users permissions to directly access the underlying base tables of the view.

What is the purpose of database views?

A database view is a subset of a database and is based on a query that runs on one or more database tables. Database views are saved in the database as named queries and can be used to save frequently used, complex queries.

What triggers SQL?

A SQL trigger is a database object which fires when an event occurs in a database. We can execute a SQL query that will “do something” in a database when a change occurs on a database table such as a record is inserted or updated or deleted. For example, a trigger can be set on a record insert in a database table.

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Are SQL views permanent?

View is a simple SQL statement that is stored in database schema (INFORMATION_SCHEMA. Views). So when ever we call the view the SQL statement gets executed and return the rows from main physical table.

How do you write a trigger?

create trigger [trigger_name]: Creates or replaces an existing trigger with the trigger_name. [before | after]: This specifies when the trigger will be executed. {insert | update | delete}: This specifies the DML operation. on [table_name]: This specifies the name of the table associated with the trigger.

How do SQL views work?

A VIEW in SQL Server is like a virtual table that contains data from one or multiple tables. It does not hold any data and does not exist physically in the database. … It contains a set of predefined SQL queries to fetch data from the database. It can contain database tables from single or multiple databases as well.

What are the uses of view?

Views can join and simplify multiple tables into a single virtual table. Views can act as aggregated tables, where the database engine aggregates data (sum, average, etc.) and presents the calculated results as part of the data. Views can hide the complexity of data.

Which of the following is the advantage of view?

A view can draw data from several different tables and present it as a single table, turning multi-table queries into single-table queries against the view.

What are the advantages and disadvantages of views in a database?

Advantages and Disadvantages of views in Sql Server

  • Security. …
  • Query Simplicity. …
  • Structural simplicity. …
  • Data Integrity. …
  • Logical data independence. …
  • Performance.
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What is SQL function with example?

Aggregate SQL Functions

Function Description
SUM() Used to return the sum of a group of values.
COUNT() Returns the number of rows either based on a condition, or without a condition.
AVG() Used to calculate the average value of a numeric column.
MIN() This function returns the minimum value of a column.

How do you run a trigger in SQL?

Procedure

  1. Write a basic CREATE TRIGGER statement specifying the desired trigger attributes. …
  2. In the trigger action portion of the trigger you can declare SQL variables for any IN, INOUT, OUT parameters that the procedure specifies. …
  3. In the trigger action portion of the trigger add a CALL statement for the procedure.
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