Transcript SQL SERVER 2005

Topics
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Views
Stored Procedures
User Defined Functions
Triggers
Views
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A view is a virtual table that consists of columns
from one or more tables
Implements a security mechanism
Complex queries can be stored in the
form as a view, and data from the
view can be extracted
using simple queries
T-SQL View
Views
CREATE VIEW [owner.]view_name
[(column_name [, column_name]...)]
[WITH ENCRYPTION]
AS select_statement [WITH CHECK OPTION]
SQL Server stores information on the view in the following system tables:
o SYSOBJECTS — stores the name of the view.
o SYSCOLUMNS — stores the names of the columns defined in the
view.
o SYSDEPENDS — stores information on the view dependencies.
o SYSCOMMENTS — stores the text of the view definition.
o Views can have up to 1024 columns.
o WITH ENCRYPTION encrypts the text for the view in the
SYSCOMMENTS tables
The restrictions imposed on views are as follows
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A view can be created only in the current database.
The name of a view must not be the same as that of the base
table they must follow the rules for identifiers.
A view can be created only if there is a SELECT permission
on its base table.
A SELECT INTO statement cannot be used in view
declaration statement.
The CREATE VIEW statement cannot be combined with
other SQL statements in a single batch.
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SCHEMABINDING – Binds views to underlying tables.
The view may have to be modified or dropped to remove
dependency on table
• If a view is not created with schemabinding clause
sp_refreshview should be run when underlying table
changes.
WITH CHECK OPTION – is an optional clause on the CREATE
VIEW statement that specifies the level of checking to be done
when inserting or updating data through a view. If the option is
specified, every row that is inserted or updated through the view
must conform to the definition of that view
Alter Views
Drop Views
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When a view is dropped, it has no effect on the underlying tables.
Dropping a view removes its definition and all the permissions
assigned to it.
However, dropping a table that references a view does not drop the
view automatically. You must drop it explicitly.
Rename View
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You can rename a view without having to drop it. This
ensures that the permissions on the view are not lost
Modifying Data using Views
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A view may be derived from multiple underlying tables
A single data modification statement that affected both the underlying
tables is not permitted.
You cannot modify the following of Columns using a view:
 Columns that are based on computed values. E.g. sum, avg
 Columns that are based on row aggregate functions. E.g. group by,
having
 Columns based on built-in functions like numeric, string functions.
Optimizing performance using Views
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Indexed Views
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You can significantly improve performance by creating a unique clustered index on a
view that involves complex processing of large quantities of data, such as aggregating or
joining many rows
Aggregations can be precompiled and stored in the index to minimize expensive
computations during query execution
Unique clustered index is created on the view, the view's result set is materialized
immediately and persisted in physical storage in the database, saving the overhead of
performing this costly operation at execution time.
When to Use Indexed Views
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Because indexed views are more complex to maintain than indexes on base tables, you
should use them only when the improved speed in retrieving the results outweighs the
increased overhead of data modifications.
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Indexing views is not a good idea in a high-volume OLTP system.
Indexed views work best when the data is relatively static, and you need to process many
rows or the view will be referenced by many queries.
Indexed Views in SQL Server 2005
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SQL Server 2005 contains many improvements for indexed views
compared with SQL Server 2000.
 Scalar aggregates, including SUM and COUNT_BIG without GROUP
BY.
 Scalar expressions and user-defined functions (UDFs)
 Common Language Runtime (CLR) types.
 User-defined types (UDTs)
 UDFs based on the CLR
 Database Tuning Advisor - recommends indexed views in addition to
recommending indexes on base tables, and table and index
partitioning strategies
Requirements for Indexed Views
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Set the ANSI_NULLS option to ON when you create the tables referenced by the view
Set the ANSI_NULLS and QUOTED_IDENTIFIER options to ON prior to creating the
view
The view must only reference base tables, not any other views
Base tables referenced by the view must be in the same database as the view and must
have the same owner
Create the view and any user-defined functions referenced in the view with the
SCHEMABINDING option. This means that the underlying tables or other database
objects cannot be altered or dropped as long as the view or function exists.
Reference all table names and user-defined functions with two-part names only—for
example, "dbo.Customers" for the Customers table.
Any functions used by the view must be deterministic, meaning that the function must
always return the same result anytime it's called with the same set of input values.
A unique clustered index must be created before any other indexes can be created on the
view.
Additional disk space will be required to hold the data defined by the indexed view.
The following Transact-SQL syntax elements are illegal in an indexed view
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The * syntax to specify all columns. Column names must be explicitly stated.
Repeated columns—for example, SELECT Col1, Col2, Col1 AS Col. However, you can reuse a column if it's part of a different expression—for example, SELECT Col1, AVG(Col1),
Col1 + Col2 AS Total
Derived tables and sub queries
ROWSET.
UNION.
OUTER JOINS OR SELF JOINS.
TOP AND ORDER BY.
DISTINCT.
COUNT(*). USE COUNT_BIG(*) INSTEAD, which returns a big int data type is allowed.
The following aggregate functions: AVG, MAX, MIN, STDEV, STDEVP, VAR.
The definition of indexed view must be deterministic
CREATE TABLE T(a int, b real, c as getdate(), d as a+b)
CREATE VIEW VT WITH SCHEMABINDING AS SELECT a, b, c, d FROM dbo.T
SELECT object_id('VT'), COLUMNPROPERTY(object_id('VT'),'d','IsPrecise')
Examples
TSQL Stored Procedures
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Precompiled execution. SQL Server compiles each stored procedure
once and then reutilizes the execution plan. This results in tremendous
performance boosts when stored procedures are called repeatedly.
Reduced client/server traffic. Stored procedures can reduce long SQL
queries to a single line that is transmitted over the wire hence reduce
client server traffic.
Efficient reuse of code and programming abstraction.
Enhanced security controls. You can grant users permission to execute a
stored procedure.
Create / Alter Syntax
Rename Stored Procedure
Drop Procedure
Execute Stored Procedure
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EXECUTE procedure_name
Parameterized Procedures
Error Handling in Stored Procedure
@@ERROR - This function is used to implement error handling code. It
contains the error ID produced by the last SQL statement executed during a
client’s connection. When a statement executes successfully, @@ERROR
contains 0. To determine if a statement executes successfully, an IF statement is
used to check the value of the function immediately after the target statement
executes. It is imperative that @@ERROR be checked immediately after the
target statement, because its value is reset when the next statement executes
successfully
RAISERROR- The RAISERROR statement is used to produce an ad hoc error
message or to retrieve a custom message that is stored in the sysmessages table.
Try..Catch Block
Implements error handling for Transact-SQL that is similar to the exception handling in the
programming languages. A group of Transact-SQL statements can be enclosed in a TRY block.
If an error occurs in the TRY block, control is passed to another group of statements that is
enclosed in a CATCH block.
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TRY…CATCH constructs can be nested. Either a TRY block or a CATCH block can contain
nested TRY…CATCH constructs.
A TRY block must be immediately followed by an associated CATCH block. Including any
other statements between the END TRY and BEGIN CATCH statements generates a syntax
error.
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A TRY…CATCH construct cannot span multiple blocks of Transact-SQL statements. For
example, a TRY…CATCH construct cannot span two BEGIN…END blocks of Transact-SQL
statements
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In the scope of a CATCH block, the following system functions can be used to obtain
information about the error that caused the CATCH block to be executed:
 ERROR_NUMBER() returns the number of the error.
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ERROR_SEVERITY() returns the severity.
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ERROR_STATE() returns the error state number.
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ERROR_PROCEDURE() returns the name of the stored procedure or trigger
where the error occurred.
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ERROR_LINE() returns the line number inside the routine that caused the error.
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ERROR_MESSAGE() returns the complete text of the error message. The text
includes the values supplied for any substitutable parameters, such as lengths,
object names, or times.
User defined functions (UDF)
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Acts like a function in programming language. Can be
parameterized and called any number of times.
Faster execution, Reduces network traffic.
The ability for a function to act like a table (for Inline table and
Multi-statement table functions) gives developers the ability to
break out complex logic into shorter and shorter code blocks.
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Three types of UDFs
 Scalar UDFs
 Inline Table valued UDFs
 Multi-statement table valued UDFs
Scalar UDFs
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UDF returns a scalar data type. Text, ntext, image,
timestamp are not supported.
Inline Table Valued UDFs
An Inline Table-Value user-defined function returns a table data type. Its an alternative to a
view as the user-defined function can pass parameters into a T-SQL select command and
in essence provide us with a parameterized, non-updateable view of the underlying tables
Multi-Statement Table valued UDFs
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A Multi-Statement Table-Value user-defined function returns a table
and is also an exceptional alternative to a view.
The ability to pass parameters into a T-SQL select command or a
group of them gives us the capability to create a parameterized, nonupdateable view of the data in the underlying tables.
Within the create function command you must define the table
structure that is being returned.
After creating this type of user-defined function, you can use it in the
FROM clause of a T-SQL command unlike the behaviour found when
using a stored procedure which can also return record sets.
Limitations of UDFs
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UDF Prohibit Usage of Non-Deterministic Built-in Functions. However
it is allowed in SQL Server 2008.
UDF cannot Call Stored Procedure
 UDF have only access to Extended Stored Procedure.
UDFs cannot make use of dynamic SQL or temporary tables within the
code. Table variables are allowed though.
UDF can not Return XML.
UDF does not support SET options.
UDF does not Support Error Handling
 TRY/CATCH,RAISEERROR or @@ERROR are not allowed in
UDFs.
UDF is allowed to modify the physical state of a database using INSERT,
UPDATE or DELETE statements.
UDF can be called through a SQL statement without using the
EXECUTE statement.
A UDF (any of the three variations - scalar, inline or multi-statement)
cannot be used to return multiple result sets.
Triggers in SQL 2005
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A trigger is a database object that is attached to a table.
The main difference between a trigger and a stored procedure is that
the former is attached to a table and is only fired when an INSERT,
UPDATE or DELETE occurs
Guards against malicious inserts and updates.
Three types of Triggers in SQL 2005
 Instead of Triggers
 After Triggers
 Data Definition Language Triggers
DML triggers use the deleted and inserted logical (conceptual) tables.
Triggers can allow cross table references, however check constraints
allow column level constraints.
SQL Server 2000 provides four different ways to determine
the affects of the DML statements.
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The INSERTED and
DELETED tables, popularly known as MAGIC TABLES
update ()
columns_updated()
Magic Table does not contain the information about the
columns of the data-type text, ntext, or image.
Attempting to access these columns will cause an error.
update() function is used to find whether a particular column
has been updated or not. This function is generally used for
data checks. Returns a Boolean value.
Columns_Update() function returns a varbinary data type representation of the columns
updated. This function return a hexadecimal values from which we can determine which
columns in the table have been updated.
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COLUMNS_UPDATED tests for UPDATE or INSERT actions performed on multiple
columns To test for UPDATE or INSERT attempts on one column, use UPDATE().
AFTER Triggers
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Triggers that run after an update, insert, or delete can be used in several
ways:
 Triggers can update, insert, or delete data in the same or other
tables. This is useful to maintain relationships between data or to
keep audit trail information.
 Triggers can check data against values of data in the rest of the
table or in other tables.
 Triggers can use user-defined functions to activate non-database
operations. This is useful, for example, for issuing alerts or
updating information outside the database.
Can be specified only on tables not on views.
AFTER trigger is a trigger that gets executed automatically before the
transaction is committed or rolled back.
settriggerorder priority can set for AFTER triggers .
A table can have several AFTER triggers for each of the three
triggering actions i.e., INSERT, DELETE and UPDATE
If a table has multiple AFTER triggers, then you can specify
which trigger should be executed first and which trigger should
be executed last using the stored procedure sp_settriggerorder
Like stored procedures and views, triggers can also be encrypted.
The trigger definition is then stored in an unreadable form. Once
encrypted, the definition of the trigger cannot be decrypted and
cannot be viewed by anyone, including the owner of the trigger
or the system administrator.
INSTEAD OF Triggers
INSTEAD OF triggers facilitates updating Views.
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A view or table can have only one INSTEAD OF trigger for each INSERT, UPDATE
and DELETE events
DDL Triggers in 2005
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DDL triggers are fired on DDL events like Create, Alter,
Drop.
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schema_name cannot be specified for DDL or logon triggers.
ALL
 Indicates that all triggers defined at the scope of the ON clause are
disabled
DATABASE
 For a DDL trigger, indicates that trigger_name was created or modified
to execute with database scope
ALL SERVER
 For a DDL trigger, indicates that trigger_name was created or modified
to execute with server scope.
Why Triggers…?
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If the database is de-normalized and requires an automated
way to update redundant data contained in multiple tables
If customized messages and complex error handling are
required
If a value in one table must be validated against a nonidentical value in another table.
Triggers are a powerful tool that can be used to enforce the
business rules automatically when the data is modified.
Triggers can also be used to maintain the data integrity. But
they are not to maintain data integrity. Triggers should be
used to maintain the data integrity only if you are unable to
enforce the data integrity using CONSTRAINTS, RULES
and DEFAULTS.
Triggers cannot be created on the temporary tables.
More on Triggers
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DISABLE/ [ENABLE] TRIGGER Trigger_Name
ON ALL SERVER;
DISABLE TRIGGER Person.uAddress ON
Person.Address;
DISABLE TRIGGER safety ON DATABASE ;
DROP TRIGGER Trigger_Name ON ALL
SERVER;
DISABLE Trigger ALL ON ALL SERVER;
Like stored procedures triggers can also be
encrypted.
Triggers can be nested up to 32 levels.
THANK YOU