If you’re learning SQL, then you might have heard about views. Exactly what are views, and how can you use them with your database? This article will help you to understand a bit about views in SQL!
What Are SQL Views?
Views are virtual tables. A view is created by executing an SQL query. It returns a result set made of rows from all three tables when executed.
Views do not change the physical structure of the database. They are used to provide an alternative way to retrieve data. Database administrators create views to make queries easier and faster.
Views are commonly used in relational database systems. A view is an abstraction over underlying tables. It can be used to provide a simplified interface to a set of related tables. The data returned by the view may or may not match that of the original table.
In other words, views can be implemented as either materialized views or inline views. A view is defined by its name and the list of columns it contains.
Types Of View
Inline views are similar to views but they do not require any additional storage space and can be updated more frequently than materialized views. They also have some performance advantages over materialized views.
Materialized views are stored in a separate file called a materialized view definition (MVD). When you create a materialized view using the CREATE MATERIALIZED VIEW statement, it stores the actual result set into a separate file. This file is then loaded into memory on demand.
A materialized view can be queried just like any other table. However, if you want to update the materialized view, you must first drop the existing version before creating a new one with different parameters. You cannot use ALTER TABLE statements to modify a materialized view.
How Do SQL Views Work?
Views are virtual tables that contain queries. They do not store any data of their own.
A concrete table means that you create a physical copy of your data on the hard drive. A virtual table means that you store your data as an object in memory.
A view is a virtual table. You can use views to avoid repeating certain queries or calculations over and over again. Views also allow you to combine several tables into one logical table.
Uses For Views
Views are useful when you want to present subsets of your data. A view acts as an aggregate table, where the database engine calculates values such as sums or averages. Views can be used to filter out unwanted information. Views can also be joined together to form a new table.
A view is a logical construct that hides the complexity of the underlying data structure. Views take up very little storage space. Views aren’t stored in the same place as the original data.
Views can be used to protect sensitive information. Users can manipulate nested views, making it easy to perform complex joins. Without views, normalizing databases into third normal form would be much harder. View functions allow users to create abstractions.
Rows in a base table lack defined order. Rows available through a view do show up but without any default sorting.
Views are relational tables, and the relational model says that a table is a set of rows. Sets are not ordered by definition, so rows of a view are not ordered either.
Therefore, an ORDERBY clause in the view definition doesn’t make sense. The SQL standard (SQL:2003) doesn’t allow an ORDERBY clause in a sub-query of a CREATEWITH statement. But, you can sort data from a view in the same way as from any other table.
Some database management systems (DBMSs), such as Oracle Database, don’t follow this SQL standard rule.
Read-Only And Updatable Views
Updatable views are defined as those views whose schema can be mapped back to the base table schema. Database systems can perform updates on these views. Views without this feature are called read-only views. These views do not support updates.
In order to enable updates on views, we need to use INSTEAD OF triggers. An INSTEAD OF trigger is used to execute some code whenever an INSERT, UPDATE, or DELETE operation occurs on the view.
Pros And Cons Of Views
A view is a virtual table created from the real table. It helps us to simplify complex queries and reduce the number of joins needed. Security views can be used to restrict access to sensitive information. View aggregation can be used to summarize large amounts of data.
Views have a lot of advantages. You can easily use them in your application. However, there are some disadvantages too.
For example, if you want to create an application using MySQL database, then you need to know about views. You should consider these disadvantages before creating views.
Advantages Of Views
- Easy to Create
- Easier to Use
- Faster Queries
- No Need for Triggers
- Can Be Used with Different DBMS’s
- Can Be Created Dynamically
- Can Be Joined Together
- Can Filter Out Unwanted Information
- Can Protect Sensitive Data
- Saves Space
- Can Be Updated
- Can Be Deleted
Disadvantages Of Views
- Cannot Sort
- Not Stored in Same Place
- Cannot Join With Other Tables
- Cannot Have Order By Clause
When To Use SQL Views
If you are looking for performance improvement and simplification in your query, then you may want to use views. They help you to get better performance when querying. They also help you to write less complex queries.
When Not To Use SQL Views
You shouldn’t use views if they will increase the size of your database. If you are going to delete a view, then you must drop all the indexes associated with that view first. This will ensure that you won’t lose any data.
Views In SQL Server
SQL Server has some other types of view for advanced uses.
Indexed views are created using a unique key (clustered or non-clustered) and are used to optimize queries that require aggregations of large amounts of data. Indexes are most useful when there are few updates to the base tables.
A partitioned view is a type of database object used to join data from different tables together. In this case, the data appears as if from one table, but actually comes from multiple tables. Local partitioned views are created by joining tables on the same server.
In conclusion, views are very powerful tools. We hope that our article helped you to understand more about views.