SQL Server 2005 Copy

8/6/2019 SQL Server 2005 Copy

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Topics

Views

Stored Procedures

User Defined Functions Triggers


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Views

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 theform as a view, and data from the

view can be extracted

using simple queries


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T-SQL View

Views

CREATE VIEW [owner.]view_name[(column_name [, column_name]...)][WITH ENCRYPTION]AS select_statement [WITH CHECK OPTION]


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The restrictions imposed on views are as follows

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 viewdeclaration 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.


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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


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Alter Views


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Drop Views

When a view is dropped, it has no effect on the underlying tables.

Dropping a view removes its definition and all the permissionsassigned to it.

However, dropping a table that references a view does not drop the

view automatically. You must drop it explicitly.


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Rename View

You can rename a view without having to drop it. This ensures

that the permissions on the view are not lost


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Modifying Data using Views

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.


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Optimizing performance using Views

Indexed Views 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 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 theincreased overhead of data modifications.

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.


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Indexed Views in SQL Server 2005

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 torecommending indexes on base tables, and table and index partitioning

strategies


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Requirements for Indexed Views

Set the ANSI_NULLS option to ON when you create the tables referenced by the view

Set theANSI_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 theSCHEMABINDING option. This means that the underlying tables or other database objectscannot be altered or dropped as long as the view or function exists.

Reference all table names and user-defined functions with two-part names onlyfor example,"dbo.Customers" for the Customers table.

Any functions used by the view must be deterministic, meaning that the function must alwaysreturn 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.


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The following Transact-SQL syntax elements are illegal in an indexed view

The * syntax to specify all columns. Column names must be explicitly stated.

Repeated columnsfor example, SELECT Col1, Col2, Col1 AS Col. However, you can re-use a column if it's part of a different expressionfor example, SELECT Col1, AVG(Col1),Col1 + Col2 AS Total

Derived tables and sub queries

ROWSET.

UNION.

OUTER JOINS OR SELF JOINS.

TOPAND 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')


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Examples


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TSQL Stored Procedures

Precompiled execution. SQL Server compiles each stored procedure onceand then reutilizes the execution plan. This results in tremendousperformance 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 clientserver traffic.

Efficient reuse of code and programming abstraction.

Enhanced security controls. You can grant users permission to execute astored procedure.


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Create / Alter Syntax


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Rename Stored Procedure

Drop Procedure


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Execute Stored Procedure

EXECUTE procedure_name

Parameterized Procedures


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Error Handling in Stored Procedure

@@ERROR - This function is used to implement error handling code. It containsthe error ID produced by the last SQL statement executed during a clients

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


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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.


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Try..Catch Block

Implements error handling for Transact-SQL that is similar to the exception handling in theprogramming 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.

TRYCATCH constructs can be nested. Either a TRY block or a CATCH block can contain

nested TRYCATCH 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.

A TRYCATCH construct cannot span multiple blocks of Transact-SQL statements. For example,

a TRYCATCH construct cannot span two BEGINEND 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.

ERROR_SEVERITY() returns the severity.

ERROR_STATE() returns the error state number.

ERROR_PROCEDURE() returns the name of the stored procedure or trigger wherethe error occurred.

ERROR_LINE() returns the line number inside the routine that caused the error.

ERROR_MESSAGE() returns the complete text of the error message. The textincludes the values supplied for any substitutable parameters, such as lengths, objectnames, or times.


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User defined functions (UDF)

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.

Three types of UDFs

Scalar UDFs

Inline Table valued UDFs

Multi-statement table valued UDFs


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Scalar UDFs

UDF returns a scalar data type. Text, ntext, image,timestamp are not supported.


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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


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Multi-Statement Table valued UDFs

AMulti-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, non-updateable

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.


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Limitations ofUDFs

UDF Prohibit Usage of Non-Deterministic Built-in Functions. However itis 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 thecode. 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 inUDFs.

UDF is allowed to modify the physical state of a database using INSERT,

UPDA

TE 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.


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Triggers in SQL 2005

A trigger is a database object that is attachedto a table.

The main difference between a trigger and a stored procedure is that theformer is attached to a table and is only firedwhen 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.


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SQL Server 2000 provides four different ways to determine

the affects of the DML statements.

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.A

ttemptingto access these columns will cause an error.


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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.


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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.

COLUMNS_UPDATED tests for UPDATE or INSERT actions performed on multiple

columns To test for UPDATE or INSERT attempts on one column, use UPDATE().


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AFTERTriggers

Triggers that run afteran update, insert, or delete can be used in severalways:

Triggers can update, insert, or delete data in the same or other tables.This is useful to maintain relationships between data or to keep audittrail 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 updatinginformation 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 forAFTER triggers .


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A table can haveseveralAFTER triggers for each of the three

triggering actions i.e., INSERT, DELETE and UPDATE

If a table has multipleAFTER triggers, then you can specifywhich trigger should be executed first and which trigger should be

executed last using the stored procedure sp_settriggerorder


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INSTEAD OF TriggersINSTEAD OF triggers facilitates updating Views.

A view or table can have only one INSTEAD OF trigger for each INSERT, UPDATE and

DELETE events


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DDL Triggers in 2005

DDL triggers are fired on DDL events like Create, Alter,

Drop. 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.


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Why Triggers?

If the database is de-normalized and requires an automatedway to update redundant data contained in multiple tables

If customized messages and complex error handling arerequired

If a value in one table must be validated against a non-identical

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. Butthey are not to maintain data integrity. Triggers should be used

to maintain the data integrity only if you are unable to enforcethe data integrity using CONSTRAINTS, RULES andDEFAULTS.

Triggers cannot be created on the temporary tables.


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DISA

BLE/ [ENA

BLE] TRIGGER Trigger_NameON ALL SERVER;

DISABLE TRIGGER Person.uAddress ON

Person.Address;

DISA

BLE TRIGGER safety ON DA

TA

BA

SE ; DROP TRIGGER Trigger_Name ON ALL

SERVER;

DISABLE TriggerALL ON ALL SERVER;

Like stored procedures triggers can also beencrypted.

Triggers can be nested up to 32 levels.

More on Triggers


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THANKYOU

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