26th SQL Night - Oct 10, 2015

1. CHAPTER
th
SQL
NIGHT
Designing and
Implementing Views
Sotiris Karras
Fivi Panopoulou
Oct 10, 2015
26

2. • Introduction to Views
• View options
• Updatable Views
• Indexed Views
Agenda

3. Views
A view is a virtual table whose contents
are defined by a query
CREATE VIEW [ schema_name . ] view_name [ (column [ ,...n ] ) ]
[ WITH <view_attribute> [ ,...n ] ]
AS select_statement
[ WITH CHECK OPTION ]
[ ; ]
<view_attribute> ::=
{
[ ENCRYPTION ]
[ SCHEMABINDING ]
[ VIEW_METADATA ]
}

4. Views
• Query is eventually applied to the underlying object
• Views can be used for
• Simplification and customization
• Security
• Backward compatibility
• The select statement cannot include
• ORDER BY clause, unless it is used with TOP or OFFSET
• Reference to temporary table or variable
• INTO and OPTION keywords

5. CHAPTER
View Options

6. CHAPTER
• CHECK OPTION
• The CHECK OPTION in the SELECT statement of a
CREATE VIEW statement allows the user to specify rules
that any modifications against the view must be
compliant with.
• Any modifications that happen in the underlying tables
that violate the rules within the CHECK OPTION are not
visible in the view.

7. CHAPTER
• SCHEMABINDING
• The SCHEMABINDING option, binds the view to the
schema of the underlying tables.
• The SCHEMABINDING option can be used only with
objects within the same database and in the SELECT
statement the participating objects must be referenced
as (schema.object).
• Other views or tables cannot be altered or dropped if
they are participating in schemabinded views.

8. CHAPTER
• ENCRYPTION and VIEW_METADATA
• Encrypts the entries in sys.syscomments that contain the
text of the CREATE VIEW statement. Using WITH
ENCRYPTION prevents the view from being published
as part of SQL Server replication.

9. CHAPTER
DEMO
Views

10. CHAPTER
Updatable Views

11. • Views through which the data of the underlying tables
can be modified.
• Managing security privileges across multiple tables
easier.
• User can modify underlying table through the view, f he haw the
corresponding permission on the view.
Updatable Views

12. • The modifications in an UPDATE, DELETE or INSERT statement can only
reference one underlying table at a time.
• The underlying columns to be modified, must be directly referenced by the
columns of the view. Cannot update columns that are derived by aggregate
functions or other computations.
• TOP clause is not present in the SELECT statement of the view.
• The columns being modified are not affected by GROUP BY, HAVING, or
DISTINCT clauses.
• Rule of thumb: The Database engine must be able to UNAMBIGUOUSLY trace
modifications from the view to the underlying table.
Restrictions

13. • The above restrictions can be avoided by creating an INSTEAD OF trigger on
the view.
• The trigger, explicitly specifies the actions to be taken if a data modification
statement is to be made on the view.
• By using an INSTEAD OF trigger, every view can be made updatable.
Bypassing the restrictions
CREATE TRIGGER <trigger_name>
ON <view>
INSTEAD OF
{INSERT, UPDATE, DELETE}
AS <SQL_code_here>;

14. CHAPTER
DEMO
Updatable Views

15. CHAPTER
Indexed Views

16. • Indexed View: a view with a unique clustered index on it
• Indexed views are used for performance tuning
• An indexed view can be updatable
• Query optimizer can use the index to speed up queries
• Additional non-clustered indexes can be created
• Indexed views affect insert and update operations on
base tables
Indexed Views

17. • Verify SET options for session and underlying tables
• Check that the view definition is deterministic
• Create the view with SCHEMABINDING
• Create a unique clustered index on the view
Creating an Indexed View
SET OPTIONS REQUIRED VALUE
ANSI_NULLS ON
ANSI_PADDING ON
ANSI_WARNINGS ON
ARITHABORT ON
CONCAT_NULL_YIEDS_NULL ON
NUMERIC_ROUNDABORT OFF
QUOTED IDENTIFIER ON

18. • All expressions in the select list, the WHERE and the
GROUP BY clause must be deterministic
• Deterministic expression: returns the same result every
time evaluated on the same input
• Precise expression: do not contain float expressions
• Float expression can only be non-key columns
• Only precise deterministic expressions can participate in
key columns.
Deterministic Views and Precise Columns

19. • If GROUP BY is present
• the definition must contain COUNT_BIG(*)
• must not contain HAVING
• the key can reference only columns specified in the GROUP BY
clause
• CLR functions can appear in the select list, but cannot
be part of the key
• The view cannot reference objects in other databases
Restrictions

20. • The statement must not contain the following elements
Restrictions
COUNT DISTINCT * MIN, MAX
ORDER BY TOP OFFSET STDEV, STDEVP, VAR, VARP, AVG
OUTER joins Self-joins UNION,EXCEPT,INTERSECT CUBE, ROLLUP, GROUPING SETS
Subquery CTE Derived table table-valued functions
CLR user-defined aggregate
function
PIVOT, UNPIVOT APPLY text, ntext, image, XML, filestream
columns
Full-text predicates TABLESAMPLE Table variables ROWSET functions
SUM function on nullable
expression
Sparse column
sets
CHECKSUM_AGG OVER clause, which includes ranking
or aggregate window functions
… and some more restrictions and requirements
https://msdn.microsoft.com/en-us/library/ms191432.aspx#Restrictions

21. CHAPTER
DEMO
Indexed Views

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