SQL Server 2008 : Viewing and Modifying Data (part 1) - Creating Views

Creating Views

SQL Server 2008 allows you to create views of the following types:

• Standard view This view is based on one or more base tables. The view may include joins, filter restrictions (using the WHERE clause), and row count restrictions (using the TOP and ORDER BY clauses). You cannot use the ORDER BY clause in a view without specifying the TOP clause as well.

• Updateable view A view that is based on a single underlying table can be updated directly. Executing INSERT, UPDATE, DELETE, and MERGE statements on this type of view will affect the data in the underlying table. You can also define an INSTEAD OF INSERT, INSTEAD OF UPDATE, and INSTEAD OF DELETE trigger on any view, which will perform a particular action when you attempt to insert, update, or delete data in the view.

• Indexed view Sometimes it is valuable to create one or more indexes on a view in order to optimize the time it takes to query the view. Indexes can be created on views using standard CREATE INDEX syntax. Indexed views must be created with the SCHEMABINDING option (see the “Using the SCHEMABINDING Option to Lock in a View’s Underlying Schema” sidebar).

• Partitioned view A partitioned view joins data that is spread across a table partitioned horizontally—for example, if you have partitioned a table by OrderDate to store orders from five years ago and earlier in one partition, orders created within the last five years in another partition, and orders created this year in yet another partition. A partitioned view will join all the partitions together into one Orders virtual table containing data from all three partitions.

To create a view, use the CREATE VIEW statement syntax shown in Example 1.

Example 1. CREATE VIEW Statement—Syntax

CREATE VIEW [schema_name].view_name [(column_names)]
[ WITH ENCRYPTION | SCHEMABINDING ]
AS select_statement
[ WITH CHECK OPTION ]

Specifying the column_names in a view definition allows you to assign names to computed columns or to rename columns produced by the SELECT statement. This is useful for calculated columns and columns that may have ambiguous names. If you don’t specify explicit column names, the view columns will inherit the same names as the columns in the SELECT statement.

Specifying the WITH ENCRYPTION option encrypts the view definition. This also prevents the view from being used in replication.

Example 2 creates a view based on the Stars table using the SCHEMABINDING option. We then attempt to alter the underlying structure of the base table but receive an error. Figure 1 demonstrates how the same view can be created using the graphical view designer in SQL Server Management Studio.

Figure 1. Creating a View Using SQL Server Management Studio

Example 2. Working with Views

CREATE VIEW MyStarsView WITH SCHEMABINDING
AS SELECT StarName, StarType FROM dbo.Stars
WHERE SolarMass >=1;
GO
SELECT * FROM MyStarsView;
-- Results:
-- StarName   StarType
-- ---------- --------------------------------------------------
-- Deneb      White supergiant
-- Pollux     Orange Giant
-- Sun        Yellow dwarf
ALTER TABLE Stars
DROP COLUMN StarType;
GO
-- Results:
--Msg 5074, Level 16, State 1, Line 1
-- The object 'MyStarsView' is dependent on column 'StarType'.
-- Msg 5074, Level 16, State 1, Line 1
-- ALTER TABLE DROP COLUMN StarType failed because one or more objects
access this column.
-- This view is updateable, as it is based upon only one base table
UPDATE MyStarsView
SET StarType = 'White Supermassive Giant'
WHERE StarType = 'White supergiant'
GO
SELECT * FROM MyStarsView;
-- Results:
-- StarName   StarType
-- ---------- --------------------------------------------------
-- Deneb      White Supermassive Giant
-- Pollux     Orange Giant
-- Sun Yellow dwarf