unit6 programming with sql server.pdf

8/22/2019 Unit6 Programming With SQL Server.pdf

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Unit 6:Programming with SQL

Server

Pratian Technologies (India) Pvt. Ltd.www.pratian.com


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Overview

Variables

Flow control constructs

IF THEN ELSE

CASE GOTO

RETURN

WAITFOR

Basic SQLCopyright 2010 Pratian Technologieswww.pratian.com

WHILE BREAK and CONTINUE

Error Handling

Procedures Functions

Triggers

Cursors


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VARIABLES

You can store a value in a user-defined variable inone statement and then refer to it later in anotherstatement

This enables you to pass values from one statementto another


User variables are written as @var_name, where thevariable name var_name consists of alphanumericand the special character _


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VARIABLES

Syntax: DECLARE@varname1, @varname2, ... data type;

For Ex: DECLARE @Student_Id int;

DECLARE @Sname, @Cname varchar(15);


Variable assignment For variable assignments, use either SETor SELECT

SET @Sname = Krishna;

SELECT @Sname = Name FROM Students

WHERE StudentId = 1001;


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FLOW CONTROL CONSTRUCTS

Flow Control Constructs include the IF, CASE,GOTO, RETURN , WAITFOR, WHILE, BREAK andCONTINUE constructs

These constructs can contain single statement or ablock of statements using BEGIN..END

m n .


These constructs can be nested also.


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IF Statement Syntax

IF search_condition

statement_list

ELSE IF search_condition

statement_list


ELSEstatement_list

For Ex:

IF @CourseId = 1

SET @Fees = 1000;


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CASE Statement Syntax

CASE case_value

WHEN when_value THEN statement_list

[WHEN when_value THEN statement_list] ... [ELSEstatement_list]


Or

CASE

WHEN search_condition THEN statement_list

[WHEN search_condition THEN statement_list] ... [ELSEstatement_list]

END


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For Ex:

DECLARE @shipping_cost INT;

DECLARE @delivery_day INT;

SET @delivery_day = DATEPART(day, getdate());


e very_ ayWHEN 1 THENSET @shipping_cost = 20;

WHEN 2 THENSET @shipping_cost = 15;

WHEN 3 THENSET @shipping_cost = 10;

ELSESET @shipping_cost = 5;

END;


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GOTO Statement

Implements a simple code jump construct

Is used to jump to a particular line of the code


Need to define a label before we use GOTO


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GOTO Syntax[label:] statement_list

GOTO [label]

For Ex:

DECLARE @day INT;SET @day = 0;


WHILE (@day


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RETURN statement

When the RETURN key word is encountered,

statement execution ends, unconditionally Any lines following a RETURN are not executed

DECLARE @Count int


SET @Count = 0

WHILE @Count


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WAITFOR statement

Allows statement execution to be paused for a

delayed time amount, or until a specific time of day

DECLARE @Count intSET @Count = 0


WHILE @Count


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WHILE Statement

The WHILE Statement repeats the statement_list

until the search_condition evaluates to true

Syntax:


searc _con t on

BEGINstatement_list

END


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For Ex:

DECLARE @Count int

SET @Count = 0

WHILE @Count < 100

BEGIN

PRINT 'Hello World'


SET @Count = @Count + 1END


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BREAK...CONTINUE

BREAK and CONTINUE are used to exit, or

continue executing WHILE or IF statements

For Ex:


oun n

SET @Count = 0

WHILE @Count < 100

BEGIN

PRINT 'Hello World'

IF @Count = 10

BREAK;

ELSE

SET @Count = @Count + 1

END


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Please try to limit the questions to the topics discussed during the session. Thank you

.

Question Time



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ERROR HANDLING

TRY/CATCH helps to write logic separate the actionand error handling code

@@ERROR variable lets us know if any error hasbeen generated by the sql statements that havebeen executed


The code meant for the action is enclosed in theTRY block and the code for error handling isenclosed in the CATCH block

In case the code within the TRY block fails, thecontrol automatically jumps to the CATCH block


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ERROR HANDLING

Functions to be used in CATCH block are : ERROR_NUMBER: returns the error number, and is the same

value of @@ERROR.

ERROR_SEVERITY: returns the severity level of the error that

invoked the CATCH block. ERROR_STATE: returns the state number of the error.

ERROR_LINE: returns the line number where the error


.

ERROR_PROCEDURE: returns the name of the storedprocedure or trigger for which the error occurred.

ERROR_MESSAGE: returns the full message text of theerror. The text includes the values supplied for any

substitutable parameters, such as lengths, object names, ortimes


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ERROR HANDLING

Syntax:BEGIN TRY

sql_statement |statement_block

END TRYBEGIN CATCH

sql_statement |


statement_blockEND CATCH


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ERROR HANDLING

Example of TRYCATCH:BEGIN TRY

DECLARE @X INT

---- Divide by zero to generate ErrorSET @X = 1/0

PRINT 'Command after error in TRY block'END TRYBEGIN CATCH

PRINT 'Error Detected'


PRINT 'Command after TRY/CATCH blocks'

Output

Error DetectedCommand after TRY/CATCH blocks


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ERROR HANDLING

Another Example of TRYCATCH:

BEGIN TRY-- Generate a divide-by-zero error.

SELECT 1/0;END TRY

BEGIN CATCHSELECT


_ ,

ERROR_SEVERITY() AS ErrorSeverity,ERROR_STATE() AS ErrorState,

ERROR_PROCEDURE() AS ErrorProcedure,ERROR_LINE() AS ErrorLine,ERROR_MESSAGE() AS ErrorMessage;

END CATCH;GO


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ERROR HANDLING

Example of TRYCATCH: RAISERROR functionBEGIN TRY

DECLARE @MyInt INT;-- Following statement will create Devide by Zero Error

SET @MyInt = 1/0;END TRYBEGIN CATCH

DECLARE @ErrorMessage NVARCHAR(4000);SELECT @ErrorMessage = ERROR_MESSAGE();


RAISERROR (@ErrorMessage, 16, 1);END CATCH;GO

Result:Msg 50000, Level 16, State 1, Line 9

Divide by zero error encountered.


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Question Time



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PROCEDURES

Custom programming scripts with embedded SQLstatements that are stored in a compiled form andexecuted directly by the MS SQL server

Allow us to store logic [rules] on the database


vto be sent between the server and the client

Procedure names can be up to 64 characters long


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PROCEDURES

Advantages of procedures

Faster Execution:Reduced need for data transfer back andforth between a program and the database server. Note: The use of SPs does not guarantee improved speed as a lot

depends on the code inside of the SP

Reduced code redundancy: Similar code needed throughout the a lication can be written once and can be reused.


Selects, Inserts, etc.. Maintenance: If there are changes in the underlying

database schema, code changes can be localized to a fewSPs

Security: Direct access to tables by user programs is aproblem and with SPs, data access can be monitored, andlogged if necessary. Centralized security rules can beapplied


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PROCEDURES

Syntax:

CREATE PROCEDURE proc_name [proc_parameterdata_type[......]]

AS

BEGIN

routine_body here;


END

proc_name : procedure nameproc_parameter : [default | OUTPUT ] param_name type

data_type : any valid data type of Sql serverroutine_body : Valid SQL procedure statement


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PROCEDURES

If you don't specify IN, OUTPUT for the parameter, it will defaultto IN

An IN parameter is passed into the stored procedure to use

internally

An OUTPUT parameter is set within the procedure, butaccessed b the caller


The name and data type of the parameter are used in the storedprocedure for referencing and setting values going in and out ofthe procedure

The data type can be any valid data type for MS SQL


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PROCEDURES

For Ex: Without parameters

CREATE PROCEDURE GetStudents

AS

BEGIN

SELECT * FROM Students

END


With IN Parameter CREATE PROCEDURE GetFeesForStudent @StudentId INT

AS

BEGIN

SELECT Fees

FROM Students

WHERE StudentId = @StudentId

END


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PROCEDURES

With IN and OUT parameters CREATE PROCEDURE GetFeesForStudent @StudentId

INT, @TotalFees INT OUTPUT

AS

BEGIN

SELECT @TotalFees = Fees

FROM Students


tu ent = tu ent

END

Method to invoke a procedure

EXEC GetStudents; EXEC GetFeesForStudent 1001;

EXEC GetFeesForStudent 1001, @TotalFees;


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PROCEDURES

ALTER PROCEDURE A procedure can be altered once created

Syntax:

ALTER PROCEDURE proc_name [proc_parameterdata_type[......]]

AS

BEGIN


routine_body here;END

proc_name : procedure nameproc_parameter : [ default | OUT ] param_name type

data_type : any valid data type of Sql serverroutine_body : Valid SQL procedure statement

DROP PROCDURE

DROP PROCEDURE procedure_name


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USER DEFINED FUNCTIONS - UDFs

User Defined Functions are compact pieces ofTransact SQL code, which can accept parameters,and return either a value, or a table

Acts like a function in programming language. Can beparameterized and called any number of times


Simpler to invoke than Stored Procedures from insideanother SQL statement

Three types of UDFs Scalar UDFs

Inline Table valued UDFs

Multi-statement table valued UDFs


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Scalar UDF Returns scalar data type

Text, ntext, image, timestamp are not supported

Scalar UDFs have the following syntax:

CREATE FUNCTION owner.function_namearameter_name data_t e =default , n


_ _

RETURNS scalar_data_type [WITH function_option]AS BEGIN

Function_body

RETURN scalar_expression

END


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Scalar UDFs Example



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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 Provides us with a parameterized, non-updateable view of

the underlying tables


Syntax: CREATE FUNCTION owner.function_name

(parameter_name data_type [=default] [, n])

RETURNS TABLE [WITH function_option]

AS

RETURN (

SELECT_statement )


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Inline table valued UDFs Example:



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Multi-statement table valued UDFs 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 commandor a group of them gives us the capability to create aparameterized, non-updateable view of the data in theunderl in tables


Within the create function command you must define thetable structure that is being returned

After creating this type of user-defined function, you can useit in the FROM clause of a T-SQL command


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Syntax: CREATE FUNCTION owner.function_name

((parameter_name data_type [=default] [, n])

RETURNS @table_variable_name TABLE

(table_definition)[WITH function_option]

AS


Function_body

RETURN

END


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Example



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Limitations of UDFs 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 notallowed in UDFs.

UDF is not allowed to modify the physical state of a database

using INSERT, UPDATE or DELETE statements. A UDF (any of the three variations - scalar, inline or multi-statement) cannot be used to return multiple result sets.

USER DEFINED FUNCTIONS UDF


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ALTER FUNCTION UDFs can be modified using the ALTER FUNCTION

statement.

The syntax of this statement is identical to CREATE

FUNCTION, with the exception of using the ALTER keywordinstead of CREATE.


DROP FUNCTION DROP FUNCTION function_owner.function_name;

Example:

DROP FUNCTION dbo.GetCustomersByCountry

TRIGGERS


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TRIGGERS

A trigger is a database object that is attached to atable.

Is attached to a table and is onlyfired

when anINSERT, UPDATE or DELETE occurs


u u u .

Triggers are used to enforce data integrity andbusiness rules

TRIGGERS


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TRIGGERS

Syntax:

CREATE TRIGGER [owner.]trigger_name

ON[owner.] table_nameFOR[INSERT/UPDATE/DELETE] ASIF UPDATE (column_name) [{AND/OR}

PDATE L MN NAME ...


_

{ sql_statements }

TRIGGERS


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TRIGGERS

For Ex: [To insert default CourseId after student insert]. CREATE TRIGGER dbo.ins_trig ON Students

AFTER INSERT

AS

INSERT INTO StudentCourses (StudentId, CourseId)VALUES (inserted.StudentId, 1)


INSERT INTO Students (StudentId, Name, Fees, JoinDate)

VALUES (1004, Krishna Kumar S, 1000, 2010-12-05)

TRIGGERS


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TRIGGERS

INSERT Trigger

When an INSERT trigger statement is executed, new rowsare added to the trigger table and to the inserted table at the

same time.

The inserted table is a logical table that holds a copy of rows


.

The inserted table can be examined by the trigger todetermine whether or how the trigger action are carried out.

With the inserted table, inserted data can be referenced

without having to store the information to the variables.

TRIGGERS


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TRIGGERS

DELETE Trigger Rows are deleted from the table and are placed in a special

table called deleted table

UPDATE Trigger

The original rows are moved into deleted table


Updated row is inserted into inserted table and the table isbeing updated

TRIGGERS


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TRIGGERS

ALTER trigger Triggers once created can be altered

Syntax would be the same as in CREATE

Instead of CREATE, we need to use ALTER

To delete a trigger from the database

DROP TRIGGER trigger_name;


CURSORS


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CURSORS

Cursors are used when the SQL Select statement isexpected to return more than one row

Is a database object used by applications tomanipulate data in a set on a row-by-row basis


u u u

functions

Way to use cursor

Before using a cursor, it must be declared and its definitioncontains the query

Then we have to open the cursor and fetch from it

After finishing the task, we should close the cursor and

de-allocate it

CURSORS


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CURSORS

Syntax:

DECLARE CURSOR FOR

OPEN


FETCH FROM INTO,

CLOSE

DEALLOCATE

CURSORS


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CURSORS

For EX:

DECLARE @StudentId INT

DECLARE StudentCursor CURSOR LOCAL FOR

SELECT StudentId From Students

OPEN StudentCursor

FETCH NEXT FROM StudentCursor INTO @StudentId

/* READ FIRST RECORD */

WHILE @@FETCH_STATUS = 0 /* LOOP WHILE NO MORE RECORDS */


INSERT INTO StudentCourses (StudentId, CourseId)VALUES (@StudentId, 1);

FETCH NEXT FROM StudentCursor INTO @StudentId

/* READ NEXT RECORD */

END

CLOSE StudentCursor

DEALLOCATE StudentCursor

CURSORS


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CURSORS

Guidelines Try to avoid cursors whenever possible Performance

issues

Do not forget to CLOSE cursor

Do not forget to DEALLOCATE cursor once all tasks are


Keep the number of rows and columns in a cursor to aminimum

Try to use READ ONLY cursors whenever possible

Question Time


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