How to make connection with the database

If you are creating dynamic application then must be used database. Before open the connection must to create connection string with the engine or database. Various database engine available in the market, which are SQL, MYSQL, ORACLE etc. Each application have own connection string to connect with the database. In this article, we will learn about that.

How to create connection String with SQL in ASP.NET C#

In Code File

using System.Data.SqlClient;

SqlConnection con = new SqlConnection();

con.ConnectionString =ConfigurationManager.ConnectionStrings ["ConnectionString"].ToString ();
con.Open ();

Using SqlConnection class, you can connect your application with database server. This class is exist in System.Data.SqlClient namespace. ConnectionString is the property of that class, in which you should pass some parameter which is mentioned below in web.config file.

In Web.Config file

<connectionStrings>

<add name="ConnectionString" connectionString="Data Source= (LocalDB)\v11.0;AttachDbFilename=|DataDirectory|\Database.mdf;Integrated Security=True;MultipleActiveResultSets=True;Application Name=EntityFramework"
providerName="System.Data.SqlClient" />
</connectionStrings>

You can pass the ConnnectionString directly in the .cs file, but here we use web.config file for security purpose because this file is not rendered on the browser. ConnectionString take some parameters like DataSource( server name), AttachDbFilename (location of the file, where your database file exist), Integrated Security(takes windows based security). You can use Initial Catalog for database file name also username and password in place of  Integrated Security.

How to create connection String in PHP with phpmyadmin

<?php
$con = mysql_connect("localhost","root","");
if (!$con)
{
die('Could not connect: ' . mysql_error());
}

mysql_select_db("studentinfo", $con);
?>

In the above mentioned code, 'mysql_connect' is a method, in which you have to pass name of server, username of the server and password. After creating the connection you should check that is connection is ok using die method. Using 'mysql_select_db' method you can pass the name of the database for updating the data.

Data Definition Language (DDL) Triggers in SQL

A DDL trigger is fired in response to DDL statements, such as CREATE TABLE or ALTER TABLE. DDL triggers can be used to perform administrative tasks, such as database auditing.

Database auditing helps in monitoring the DDL operations on a database. DDL operation can include operations such as creation of a table or view, or modifications of a table or procedure. Consider an example, where you want the database administrator to be notified whenever a table is created in the Master Database. For this purpose, you can create a DDL trigger.

Depending on the way in which triggers are fired, they are categorized as:

After Triggers

The after trigger can be created on any table for the insert, update or delete operation just like other triggers. The main difference in the functionality of an after trigger is that it is fired after the execution of the DML operation for which it has been defined. The after trigger is executed when all the constraints and triggers defined on the table are successfully executed.

By default, if more than one after trigger is created on a table is for a DML operation such as insert, update, or delete, then the sequence of execution is the order in which they were created.
For example, the EmpSalary table stores the salary and tax details for all the employees in an organization. You need to ensure that after the salary details of an employee are updated in the EmpSalary table, the tax details are also recalculated and updated. In such a scenario, you can implement an after trigger to update the tax details when the salary details are updated.

Instead of Triggers

The instead of triggers can be primarily used to perform an action, such as a DML operation on another table or view. This type of trigger can be created on both a table as well as a view.

An instead of trigger can be used for the following actions:

• Ignoring parts of a batch.
• Not processing a part of a batch and logging the problem rows.
• Taking an alternative action when an error condition is encountered.

For example, if a view is created with multiple columns from two or more tables, then an insert operation on the view is only possible if the primary key fields from all the base tables are used in the query. Alternatively, if you use an instead of trigger, you can insert data in the base tables individually. This makes the view logically updateable.

You can even create an Instead of trigger to restrict deletion in a master table. For example, you can display a message “Master record cannot be deleted” if a delete statement is executed on the Employee table of the AdventureWorks database.

Unlike after triggers, you cannot, create more than one Instead of trigger for a DML operation on the same table or view.

Nested Triggers

Nested triggers are fired due to actions of other triggers. For example, you delete a row from TableA. A trigger on TableA deletes rows from TableB. Because you are deleting rows from TableB, a trigger is executed on TableB to record the deleted rows.

Recursive Triggers

Recursive triggers are a special case of nested triggers. Unlike nested triggers, support for recursive triggers is at the database level. As the name implies, a recursive trigger eventually calls itself. There are two types of recursive triggers, Direct and Indirect.

Direct Recursive Trigger

A direct trigger is a trigger that performs the same operation (insert, update, or delete) on the same table causing the trigger to fire itself again.

Indirect Recursive Trigger

An indirect trigger is a trigger that fires a trigger on another table and eventually the nested trigger ends up firing the first trigger again. For instance, an UPDATE on TableA fires a trigger that in turn fires an update on TableB. The update on TableB fires another trigger that performs an update on TableC. TableC has a trigger that causes an update on TableA again. The update trigger of TableA is fired again.

Execute Batches multiple times using Stored Procedures in SQL

Batches are temporary in nature. To execute a batch more than once, you need to recreate SQL statements and submit them to the server. This leads to an increase in the overhead, as the server needs to compile and create the execution plan for these statements again. Therefore, if you need to execute a batch multiple times, you can save it within a stored procedure. A stored procedure is a precompiled object stored in the database.

Stored procedures can invoke the Data Definition Language (DDL) and Data Manipulation Language (DML) statements and can return values. If you need to assign values to the variables declared in the procedures at the run time, you can pass parameters while executing them. You can also execute a procedure from another procedure. This helps in using the functionality of the called procedure within the calling procedure.

Creating Stored Procedures

You can create a stored procedure by using the CREATE PROCEDURE statement. The syntax of the CREATE PROCEDURE statement is:

CREATE PROCEDURE proc_name
AS
BEGIN
Sql_statement1
Sql_statement2
END

Where Proc_name specifies the name of the stored procedure.

The following example create a stored procedure to view the department names from the Department table:

CREATE PROCEDURE prcDept
AS
BEGIN
SELECT Name FROM HumanResources.Department
END

When the CREATE PROCEDURE statement is executed, the server compiles the procedure and saves it as a database object. The procedure is then available for various applications to execute. The process of compiling a stored procedure involves the following steps:

• The procedure is compiled and its components are broken into various pieces. This process is known as parsing.
• The existence of the referred objects, such as tables and views, are checked. This process is known as resolving.
• The name of the procedure is stored in the sysobjects table and the code that creates the stored procedure is stored in the syscomments table.
• The procedure is compiled and a blueprint for how the query will run is created. This blueprint is specified as execution plan. The execution plan is saved in the procedure cache.
• When the procedure is executed for the first time. The execution plan will be read and fully optimized and then run. The net time the procedure is executed in the same session, it will be read directly from the cache. This increases performance, as there is no repeated compilation.

After creating the stored procedure, you can view the code of the procedure by using the sp_helptext command.

Implementing Triggers and its Types in SQL

In a relational database, data in a table is related to other tables. Therefore, while manipulating data in one table, you need to verify and validate its effect on data in the related tables. In addition, you might need to manipulate data in a table after inserting or updating data in another table.

You also need to ensure that if an error occurs while updating the data in a table, the changes are reverted. This helps in maintaining data integrity. The SQL Server allows you to implement triggers and transactions to maintain data integrity.

This article explains different types of triggers that can be created in SQL Server. Next, we will discusses how to implement triggers to enforce data integrity. Further, we will discuss about how to implement transactions.

Implement Triggers

At times, while performing data manipulation on a database object, you might also need to perform another manipulation on another object. For example, in an organization, the employees use the Online Leave Approval system to apply for leaves. When an employee applies for a leave, the leave details are stored in the Leave-Details table. In addition, a new record is added to the Leaves-For-Approval table. When the supervisors log on to the system, all the leaves pending for their approval are retrieved from the Leaves-For-Approval table and displayed to them.

To perform such operations, the SQL Server allows you to implement triggers. A trigger is a block of code that constitutes a set of T-SQL statements activated in response to certain actions, such as insert or delete. Triggers are used to ensure data integrity before or after performing data manipulations.

Before you implement a trigger, it is important to know the different types of triggers that can be created by using SQL Server.

Identifying Types of Triggers

In the SQL Server, various kinds of triggers can be used for different types of data manipulation operations. The SQL Server supports the following types of triggers:

Data Modification Language (DML) triggers

A DML trigger is fired when data in the underlying table is affected by DML statements, such as INSERT, UPDATE, or DELETE. These triggers help in maintaining consistent, reliable, and correct data in tables. They enable the performance of complex action and cascade these actions to other dependent tables. Cascading is the process of reflecting the changes made in a table in the other related tables.

Data Definition Language (DDL) triggers

A DDL trigger is fired in response to DDL statements, such as CREATE TABLE or ALTER TABLE. DDL triggers can be used to perform administrative tasks, such as database auditing.

Creating Table-Valued Functions in SQL

A table-valued function returns a table as an output, which can be derived as a part of a SELECT statement. Table-valued function return the output as a table data type. The table data is a special data type used to store a set of rows, which return the result set of a table-valued function. Table-valued functions are of two types:

Inline Table-Valued Function

An inline table-valued function returns a variable of a table data type from the result set of a single SELECT statement. An inline function does not contain a function body within the BEGIN and END statements.

Consider an example where the inline table-valued function, fx_Department_GName, accepts a group name as parameter and returns the details of the departments that belong to the group from the Department table. You can create the function by using the following statement:

CREATE FUNCTION fx_Department_GName ( @GrName nvarchar (20) )
RETURNS table
AS
RETURN (
SELECT *
FROM HumanResources.Department
WHERE GroupName=@GrName
)
GO

You can use the following statement to execute the fx_Department_Gname function with a specified argument:

SELECT * FROM fx_Department_GName (‘Manufacturing’)

The preceding statement will return a result set having the group name ‘Manufacturing’.

Consider another example of an inline function that accepts rate a a parameter and returns all the records that have a rate value greater than the parameter value:

CREATE FUNCTION HumanResources.Emp_Pay (@Rate int)
RETURNS table
AS
RETURN (
SELECT e.EmployeeID, e.Title, er.Rate
FROM HumanResources.Employee AS e
JOIN HumanResources.EmployeePayHistory AS er
ON e.EmployeeID=er.EmployeeID WHERE er.Rate<@Rate
)
GO
The preceding function will return a result set that displays all the records of the employees who have the pay rate greater that the parameter.

Multistatement Table-Valued Function

A Multistatement table-valued function uses multiple statements to build the table that is returned to the calling statement. The function body contains a BEGIN…END block, which holds a series of T-SQL statements to build and insert rows into a temporary table. The temporary table is returned in the result set and is created based on the specification mentioned in the function.

Consider an example where the Multistatement table-valued function, PayRate, is created to return a set of records from the EmployeePayHistory table by using the following statements:

CREATE FUNCTION PayRate (@rate money)
RETURNS @table TABLE
(EmployeeID int NOT NULL,
RateChangeDate datetime NOT NULL,
Rate money NOT NULL,
PayFrequency tinyint NOT NULL,
modifiedDate datatime NOT NULL)
AS
BEGIN
INSERT @table
SELECT *
FROM HumanResources.EmployeePayHistory
WHERE Rate > @rate
RETURN
END

The function returns a result set in from of a temporary table, @table, created within the function. You can execute the function by using the following statement:

SELECT * FROM PayRate (45)

Depending on the result set returned by a function can be categorized as deterministic or nondeterministic. Deterministic functions always return the same result whenever they are called with a specific set of input values. However, nondeterministic function may return different results each time they are called with a specific set of input values.

An example of a deterministic function is date add, which returns the same result for any given set of argument values for its three parameters. Get date is a nondeterministic function because it is always invoked without any argument, but the return value changes on every execution.

Creating Scalar functions in SQL

In earlier article we have discussed about user defined functions that have the limited scope in sql programming in compare to stored procedures. User defined function have two types i.e. scalar function and table-valued function. In this article we will discuss about scalar functions.

Scalar function accept a single parameter and return a single data value of the type specified in the RETURNS clause. A scalar function can return any data type except text, ntext, image, cursor, and timestamp. Some scalar functions, such and current_timestamp, do not require any arguments.

A function contains a series of T-SQL statements defined in a BEGIN…END block of the function body that returns a single value.

Consider an example of a scalar function that calculates the monthly salary of the employees accepting the pay rate as an input and returning a single value after multiplying the value with the number of hours and number of days:

CREATE FUNCTION HumanResources.MonthlySal (@PayRate float)
RETURN float
AS
BEGIN
RETURN (@PayRate * 8 * 30)
END

You can execute this function by using the following statements:

DECLARE @PayRate float
SET @PayRate = HumanResources.MonthlySal (12.25)
PRINT @PayRate

In the preceding code, @PayRate is a variable that will store a value returned by the MonthlySal function.

How to Implement User Defined Function in SQL

Similar to the stored procedures, you can also create functions to store a set of T-SQL statements permanently. These functions are also referred to as user-defined functions (UDFs). A UDF is a database object that contains a set of T-SQL statements, accepts parameters, performs an action, and returns the result of that action as a value. The return value can either be a single scalar value or a result set.

UDFs have a limited scope as compared to stored procedures. You can create functions in situations when you need to implement a programming logic that does not involve any permanent changes to the database objects outside the function. For example, you cannot modify a database table from a function.

UDFs are of different types: scalar functions and table-valued function. As a database developer, it is important for you to learn to create and manage different types of UDFs.

Creating UDFs

A UDF contains the following components:

• Function name with optional schema/owner name
• Input parameter name and data type
• Options applicable to the input parameter
• Return parameter data type and optional name
• Options applicable to the return parameter
• One or more T-SQL statements

To create a function, you can use th CREATE FUNCTION statement. The syntax of the CREATE FUNCTION statement is:

CREATE FUNCTION [ schema_name. ] function_name
( [ { @parameter_name [AS ] [ type_schema_name. ]
Parameter_data_type] }
[ = default ] }
[, …n ]
]
)
RETURNS return_data_type
[WITH <function_option> [ , . . .n ] ]
[ AS ]
BEGIN
Function_body
RETURN expression
END
[;]
Where,

• Schema_name is the name of the schema to which the UDF belongs.
• Function_name is the name of the UDF. Function names must comply with the rules for identifiers and must be unique within the database and to its schema.
• @parameter_name is a parameter in the UDF. One or more parameters can be declared.
• [type_schema_name.] parameter_data_type is the data type of the parameter, and optionally the schema to which it belongs.
• [=default ] is a default value for the parameter.
• Return_data_type is the return value of a scalar user-defined function.

Calling a Procedure from another Procedure: SQL

At times, you might need to use the values returned by a procedure in another procedure. For this, you can execute or call one procedure from within another procedure.

A procedure that calls or executes another procedure is known as the calling procedure, and the procedure that is called or executed by the calling procedure is termed as the called procedure. You can also execute a procedure from another procedure if you need to use the functionality provide by one into another.

Consider the previous example where the prcGetEmployeeDetail procedure returns the employee details for a given employee ID. You can create the prcDisplayEmployeeStatus procedure, which accepts the employee ID of an employee as input and displays the department name and shift ID where the employee is working along with the manager ID and the title employee. To perform this task, you need to call the prcGetEmployeeDetail procedure from the prcDisplayEmployeeStatus procedure, as shown in the following statement:

CREATE PROCEDURE prcDisplayEmployeeStatus @EmpId int
AS
BEGIN
DECLARE @DepName char (50)
DECLARE @ShiftId int
DECLARE @ReturnValue int
EXEC @ReturnValue = prcGetEmployeeDetail @EmpId,
@ DepName OUTPUT,
@ ShiftId OUTPUT
IF (@ReturnValue = 0)
BEGIN
PRINT ‘The details of an employee with ID: ‘ + convert (char (10), @EmpId)
PRINT ‘shift ID: ‘ + convert ( char (1), @shiftId)
SELECT ManagerID, Title FROM HumanResources.Employee
WHERE EmployeeID = @EmpID
END
ELSE
PRINT ‘No records found for the given employee’
END

To execute the preceding code, you need to execute the following statement:
EXEC prcDisplayEmployeeStatus 2

SQL Server provides a function, @@ROWCOUNT, which return the number of rows affected by the last statement. You can use this statement in the IF construct to check the result of the last statement that executed.