Skip to main content

Views - SQL Server

 Views

A view in SQL Server is a virtual table that is based on the result of a select statement. Views can simplify complex queries, hide the complexity of the underlying data model, and provide a security mechanism by limiting access to sensitive data. In addition, views can be used to provide a consistent view of data across multiple tables or to present a subset of data that is tailored to a specific application or user.

Creating a view in SQL Server is straightforward. Here's an example:

CREATE VIEW CustomersWithOrders AS

SELECT c.CustomerID, c.CompanyName, COUNT(o.OrderID) AS OrderCount

FROM Customers c

LEFT JOIN Orders o ON c.CustomerID = o.CustomerID

GROUP BY c.CustomerID, c.CompanyName;

In this example, we're creating a view called CustomersWithOrders that contains three columns: CustomerID, CompanyName, and OrderCount. The view is based on a select statement that joins the Customers and Orders tables and groups the results by customer ID and company name.

To modify a view in SQL Server, you can use the ALTER VIEW statement. Here's an example:

ALTER VIEW CustomersWithOrders

AS

SELECT c.CustomerID, c.CompanyName, COUNT(o.OrderID) AS OrderCount, AVG(o.TotalAmount) AS AvgAmount

FROM Customers c

LEFT JOIN Orders o ON c.CustomerID = o.CustomerID

GROUP BY c.CustomerID, c.CompanyName;

 

In this example, we're modifying the CustomersWithOrders view to include a new column that calculates the average order amount for each customer. The ALTER VIEW statement is used to update the definition of the view to include this new column.

Note that when you modify a view, you need to ensure that the changes do not violate any existing constraints or dependencies. For example, if the view is used in other queries or in stored procedures, you may need to modify those objects as well to ensure that they continue to work correctly with the updated view.

 Indexed View

In SQL Server, an indexed view is a view that has been materialized and stored in the database as a physical index. Indexed views can improve query performance by pre-aggregating data and reducing the number of joins required to satisfy a query.

To create an indexed view in SQL Server, follow these steps:

  1. Create a view that contains the desired query logic. For example:

CREATE VIEW SalesByProduct AS

SELECT ProductID, SUM(OrderQty) AS TotalSales

FROM SalesOrderDetail

GROUP BY ProductID;

  1. Add the WITH SCHEMABINDING option to the view definition. This option ensures that the schema of the underlying tables cannot be modified while the indexed view exists.

 

ALTER VIEW SalesByProduct WITH SCHEMABINDING AS

SELECT ProductID, SUM(OrderQty) AS TotalSales

FROM SalesOrderDetail

GROUP BY ProductID;

 

  1. Create a clustered index on the view. This index will be used to store the materialized data and support queries against the view.

     CREATE UNIQUE CLUSTERED INDEX IX_SalesByProduct ON SalesByProduct (ProductID);


In this example, we're creating a clustered index on the SalesByProduct view, using the ProductID column as the index key. The index is marked as unique, since each product should have only one total sales value.Note that creating an indexed view can have some performance implications, as it requires additional storage and maintenance overhead. However, for certain types of queries and data models, indexed views can be an effective way to improve query performance.

Delete the view

              To delete a view in SQL Server, you can use the DROP VIEW statement followed by the name of the view you want to delete. Here's an example:

 DROP VIEW CustomersWithOrders;

In this example, we're deleting the CustomersWithOrders view. Once the view is deleted, any dependent objects such as stored procedures or other views that use the view will also be affected and may need to be updated or deleted as well.

It's important to note that once a view is deleted, it cannot be recovered. So be sure to double-check that you have selected the correct view before deleting it.

 Reference

              https://learn.microsoft.com/en-us/sql/relational-databases/views/views?view=sql-server-ver16

Labels:

Comments

Post a Comment

Popular posts from this blog

Data type precedence - SQL Server

       In SQL Server, data type precedence determines which data type takes precedence over others when two or more data types are combined or compared. It is important to understand data type precedence to ensure that the correct data type is used and that data is not lost or truncated during operations. In this blog, we will discuss data type precedence in SQL Server with examples. Data type precedence levels SQL Server has 16 data type precedence levels, with the highest level being 1 and the lowest level being 16. The data type with the lowest precedence is considered to be the "weakest" data type and is most likely to be converted to a higher precedence data type during operations. Here is the list of data types in SQL Server, ordered by their precedence levels: user-defined data types (highest precedence) sql_variant xml datetimeoffset datetime2 datetime smalldatetime date time float real decimal/numeric money/smallmoney bigint/i...
Post a Comment
Read more

Synonyms, Trigger & Sequences - SQL Server

  Synonyms In SQL Server, a synonym is an alternative name for a database object, such as a table, view, stored procedure, or function. Synonyms can be useful for simplifying complex object names, abstracting the underlying object structure, or providing a layer of indirection between objects and their callers. Creating a synonym in SQL Server is straightforward. Here's an example:               CREATE SYNONYM MyTable FOR AdventureWorks2019 . dbo . MyTable ; In this example, we're creating a synonym called MyTable that points to a table called MyTable in the AdventureWorks2019 database. Now, instead of referring to the table as AdventureWorks2019.dbo.MyTable, we can simply use the synonym name MyTable. To modify a synonym in SQL Server, you can use the ALTER SYNONYM statement. Here's an example:               ALTER SYNONYM MyTable RENA...
Post a Comment
Read more

Table Data Type- SQL Server

       In SQL Server, the table data type is a structured data type that allows you to define a table as a variable. It can be useful in scenarios where you need to store data temporarily or pass data between stored procedures or functions. In this blog, we will explore the table data type in SQL Server and provide an example of how it can be used. Introduction to the table data type The table data type is a structured data type that allows you to define a table as a variable. It can be used to store data temporarily or pass data between stored procedures or functions. The table variable behaves like a regular table in SQL Server, but it is stored in memory rather than on disk. Creating a table variable in SQL Server To create a table variable in SQL Server, you need to declare the variable and define the table structure. The following code demonstrates how to declare a table variable and define the table structure: DECLARE @MyTable TABLE (   ...
Post a Comment
Read more