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European SQL 2012 Hosting - Nederland :: Check SQL Memory Usage by Builing a Report

clock February 17, 2014 07:12 by author Scott

Memory is one of the most-used resources in SQL Server. Generally, the more you have, the better query performance you’ll get. How can you track your server’s memory usage? One way is to use the Performance Monitor (Perfmon) counters exposed through the sys.dm_os_performance_counters DMV. One indicator of memory performance is Page Life Expectancy (PLE). You can capture basic memory usage over time by setting up a SQL Server Agent job to query this DMV, inserting the results into a table, and reporting on the table results.

COLLECTING THE DATA

I have a “DBAInfo” database on my instance that I use to track metrics and other information. I create a new table, MemoryHistory.

USE DBAInfo;
CREATE TABLE MemoryHistory
(ID INT IDENTITY NOT NULL,
CollectionDateTime DATETIME,
PerfmonObjectName NCHAR(128),
CounterName NCHAR(128),
CounterValue BIGINT)

Then, I create a new SQL Server Agent job that runs every 5 minutes.

The only step in this job is the below query, which queries the DMV and inserts the results into the table I created.

INSERT INTO MemoryHistory
SELECT CURRENT_TIMESTAMP,
object_name,
counter_name,
cntr_value
FROM sys.dm_os_performance_counters
WHERE object_name = 'SQLServer:Buffer Manager';

I schedule the job to run every five minutes.

VIEWING THE DATA

Now, this data isn’t going to do me any good unless I view it, and make a decision or perform an action based on what I learn.

To view the data I’ve collected, I run the following query:

SELECT ID,
CollectionDateTime,
CounterName,
CounterValue
FROM MemoryHistory;

That’s a lot of junk to sort through when all I want to see is PLE, so I narrow down the query a bit.

SELECT ID,
CollectionDateTime,
CounterName,
CounterValue
FROM MemoryHistory
WHERE CounterName = 'Page life expectancy';

But who wants to read through results like that each time there’s a problem to see when PLE rose or fell? Not me. I’d rather see it in a graphical format. How can I do that?

SQL Server Reporting Services

I have SSRS at my disposal. I’m going to create a very simple report that will allow me to enter start and end dates, and will display a line chart for PLE during that time.

REPORTING ON THE DATA

I set up my report to have DBAInfo as my data source. In order to choose dates, I use the following query as my dataset.

SELECT ID,
CollectionDateTime,
CounterName,
CounterValue
FROM MemoryHistory
WHERE CounterName = 'Page life expectancy'
AND CONVERT(DATE, CollectionDateTime) >= @Start
AND CONVERT(DATE, CollectionDateTime) <= @End;

I change my @Start and @End parameters to “Date/Time” so I get a date picker.

I drag a Line Chart onto the design surface and add the CounterValue as my Value and CollectionDateTime as my Category Group.

I can preview the report to view it:

Last but not least, I’ll deploy this report to Report Manager so that I and others can run it, or even schedule a regular subscription.



European SQL Hosting - Amsterdam :: Difference Between Stored Procedure and Function in SQL Server

clock October 28, 2013 08:44 by author Scott

Today post I will show you the difference between Stored Procedure and Function in SQL Server. Stored Procedures are pre-compile objects which are compiled for first time and its compiled format is saved which executes (compiled code) whenever it is called. But Function is compiled and executed every time when it is called.

Basic Difference

  • Function must return a value but in Stored Procedure it is optional( Procedure can return zero or n values).
  • Functions can have only input parameters for it whereas Procedures can have input/output parameters .
  • Function takes one input parameter it is mandatory but Stored Procedure may take o to n input parameters..
  • Functions can be called from Procedure whereas Procedures cannot be called from Function.

Advance Difference

  1. Procedure allows SELECT as well as DML(INSERT/UPDATE/DELETE) statement in it whereas Function allows only SELECT statement in it.
  2. Procedures can not be utilized in a SELECT statement whereas Function can be embedded in a SELECT statement.
  3. Stored Procedures cannot be used in the SQL statements anywhere in the WHERE/HAVING/SELECT section whereas Function can be.
  4. Functions that return tables can be treated as another rowset. This can be used in JOINs with other tables.
  5. Inline Function can be though of as views that take parameters and can be used in JOINs and other Rowset operations.
  6. Exception can be handled by try-catch block in a Procedure whereas try-catch block cannot be used in a Function.
  7. We can go for Transaction Management in Procedure whereas we can't go in Function.

Hope it will completely enough to explain the difference about stored procedure and Function.



European SQL 2012 Hosting - Italy :: SQL Server 2012 Function

clock October 1, 2013 10:21 by author Scott

Here, I have provided an article showing you how to utilize the two new logical functions Choose and IIF in SQL Server. The Choose function works like an array kind of thing and the IIF function is used to check a condition. In this article we will see both functions with examples. These functions are also called new logical functions in SQL Server 2012. So let's take a look at a practical example of how to use the Choose and IIF functions in SQL Server. The example is developed in SQL Server 2012 using the SQL Server Management Studio.

These are the two logical functions:

1. IIF() Function
2. Choose() Function

IIF() Function

The IIF function is used to check a condition. Suppose X>Y. In this condition a is the first expression and b is the second expression. If the first expression evaluates to TRUE then the first value is displayed, if not the second value is displayed.

Syntax

IIF ( boolean_expression, true_value, false_value )

Example

DECLARE @X INT;
SET @X=50;
DECLARE @Y INT;
SET @Y=60;
Select iif(@X>@Y, 50, 60) As IIFResult

In this example X=50 and Y=60; in other words the condition is false.  Select iif(@X>@Y, 50, 60) As IIFResult. It returns false value that is 60.

Output

Choose() Function

This function is used to return the value out of a list based on its index number. You can think of it as an array kind of thing. The Index number here starts from 1.

Syntax

CHOOSE ( index, value1, value2.... [, valueN ] )

CHOOSE() Function excepts two parameters,

Index: Index is an integer expression that represents an index into the list of the items. The list index always starts at 1. 

Value: List of values of any data type.

Now some facts related to the Choose Function

1. Item index starts from 1

DECLARE @ShowIndex INT;
SET @ShowIndex =5;
Select Choose(@ShowIndex, 'M','N','H','P','T','L','S','H') As ChooseResult 

In the preceding example we take index=5. It will start at 1. Choose() returns T as output since T is present at @Index location 5.

Output

2.  When passed a set of types to the function it returns the data type with the highest precedence; see:

DECLARE @ShowIndex INT;
SET @ShowIndex =5;
Select Choose(@ShowIndex ,35,42,12.6,14,15,18.7)  As CooseResult

In this example we use index=5. It will start at 1. Choose() returns 15.0 as output since 15 is present at @ShowIndex location 5 because in the item list, fractional numbers have higher precedence than integers.

3. If an index value exceeds the bound of the array it returns NULL

DECLARE @ShowIndex INT;
SET @ShowIndex =9;
Select Choose(@ShowIndex , 'M','N','H','P','T','L','S','H')  As CooseResult

In this example we take index=9. It will start at 1. Choose() returns Null as output because in the item list the index value exceeds the bounds of the array; the last Index=8.

Output

4. If the index value is negative then that exceeds the bounds of the array therefore it returns NULL; see:

DECLARE @ShowIndex INT;
SET @ShowIndex =-1;
Select Choose(@ShowIndex, 'M','N','H','P','T','L','S','H')  As CooseResult

In this example we take index= -1. It will start at 1. Choose() returns Null as output because in the item list the index value exceeds the bounds of the array.

Output

5. If the provided index value has a float data type other than int, then the value is implicitly converted to an integer; see:

DECLARE @ShowIndex  INT;
SET @ShowIndex =4.5;
Select Choose(@ShowIndex ,35,42,12.6,13,15,20) As CooseResult

In this example we take index= 4.5. It will start at 1.  If the specified index value has a float data type other than int, then the value is implicitly converted to an integer. It returns the 13.0 as output since 15 is present at @ShowIndex=4.5 which means index is 4.

Output



European SQL Hosting - Amsterdam :: SQL Injection? How to Prevent It?

clock June 19, 2013 08:10 by author Scott

This article talk about what SQL injection is, how can that effect the security of our websites and what steps should be taken to create an ASP.NET application SQL injection proof. SQL injection is the attack in which the user of the website will input some SQL code as input which would result in creating a SQL statement that developers didn't intend to write. These SQL statements could result in unauthorized access, revealing secret user information and sometimes it could even wipe out the entire data lying on the server.

 

Getting to know SQL Injection

Let us take this discussion a little further by looking into the bad coding practices that will make the application prone to the SQL injection attacks. Let us create a simple table that contains username and password of the user for authentication.

Now I will create a small page that lets the user to enter his login credentials and get them validated against the Users table.

Note: Password should never be stored in plain text. This table contains password in plain text just for the sake of simplicity of this article.

The actual code that I will use to authenticate the user contains dynamic SQL that is being created by concatenating strings. This code will return true if the userid and password are found in the database otherwise false.  

public bool IsUserAuthenticated_Bad(string username, string password)
{
    DataTable result = null;
    try
    {
        using (SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["SampleDbConnectionString1"].ConnectionString))
        {
            using (SqlCommand cmd = con.CreateCommand())
            {
                cmd.CommandType = CommandType.Text;
                cmd.CommandText = "select userID from Users where userID = '" + username + "' and password = '" + password + "'";               

                using (SqlDataAdapter da = new SqlDataAdapter(cmd))
                {
                    result = new DataTable();
                    da.Fill(result);


                    //check if any match is found
                    if (result.Rows.Count == 1)
                    {
                        // return true to indicate that userID and password are matched.
                        return true;
                    }
                }
            }
        }
    }
    catch (Exception ex)
    {
        //Pokemon exception handling
    }

    //user id not found, lets treat him as a guest       
    return false;
}

For all the normal users this code will work fine. I can even test it using userid as sampleuser and password as samplepwd and this will work fine. For any other data except this it should say that authentication failed(since this is the only record in the table). The query that will get generated to test this input will be:

select userID from Users where userID = 'sampleuser' and password = 'samplepwd'

Now let us try to inject some SQL into this page. Let me give hacker' or 1=1-- as username and anything in the password(even leave it empty). Now the resultant SQL for this will become:

select userID from Users where userID = 'hacker' or 1=1--' and password = ''

Now when we execute this query the 1=1 clause will always return true(and the password check is commented out. Now irrespective of whatever data user has entered this will SQL return a row making this function return true and in turn authenticating the user. So What I have done now is that I gained access to the website even when I didn't knew the valid user credentials.

How can I curb this problem is something we will look into details in some time. But before that let us also look at one more example of SQL injection just to get little more understanding.

In this second example we will assume that the malicious user somehow got hold of the database schema and then he is trying to manipulate the application to find some confidential information. Lets say we have a page that is supposed to show all the products that are assigned to a user in the organization.

Let us start by looking at the Product table.

Let us now look at the code that is retrieving this data:

public DataTable GetProductsAssigner_Bad(string userID)
{
    DataTable result = null;
    try
    {
        using (SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["SampleDbConnectionString1"].ConnectionString))
        {
            using (SqlCommand cmd = con.CreateCommand())
            {
                cmd.CommandType = CommandType.Text;
                cmd.CommandText = "select * from Products where AssignedTo = '" + userID + "'";

                using (SqlDataAdapter da = new SqlDataAdapter(cmd))
                {
                    result = new DataTable();
                    da.Fill(result);
                }
            }
        }
    }
    catch (Exception ex)
    {
        //Pokemon exception handling
    }

    //user id not found, lets treat him as a guest       
    return result;
}

Now if I call this function with the proper data(as normal users would do) then this will show me the results. i.e. If I call this page for sampleuser the resulting query would be:

select * from Products where AssignedTo = 'sampleuser'

Now let me use this query string with this page: userID=' UNION SELECT 0 AS Expr1, password, userID FROM Users -- . Once this data is used with the current code this will show me all the username and passwords from the database. The reason will be quiet clear once we look into the resulting query of this input.

select * from Products where AssignedTo = '' UNION SELECT 0 AS Expr1, password, userID FROM Users --

Now we saw that how string concatenated dynamic SQL is prone to SQL injection. There are many other problems that could be created by injecting SQL. Imagine a scenario where the injected SQL is dropping tables or truncating all the tables. The problem in such cases would be catastrophic.

How to Prevent SQL Injection

ASP.NET provides us beautiful mechanism for prevention against the SQL injection. There are some thumb rules that should be followed in order to prevent injection attacks on our websites.

  • User input should never be trusted. It should always be validated
  • Dynamic SQL should never be created using string concatenations.
  • Always prefer using Stored Procedures. 
  • If dynamic SQL is needed it should be used with parametrized commands.
  • All sensitive and confidential information should be stored in encrypted.
  • The application should never use/access the DB with Administrator privileges. 

User input should never be trusted. It should always be validated

The basic thumb rule here is that the user input should never be trusted. First of all we should apply filters on all the input fields. If any field is supposed to take numbers then we should never accept alphabets in that. Secondly, All the inputs should be validated against a regular expression so that no SQL characters and SQL command keywords are passed to the database.

Both this filtration and validation should be done at client side using JavaScript. It would suffice for the normal user. Malicious users cans till bypass the client side validations. So to curb that all the validations should be done at server side too.

Dynamic SQL should never be created using string concatenations.

If we have dynamic SQL being created using string concatenations then we are always at the risk of getting some SQL that we are not supposed to use with the application. It is advisable to avoid the string concatenations altogether.

Always prefer using Stored Procedures.

Stored procedures are the best way of performing the DB operations. We can always be sure of that no bad SQL is being generated if we are using stored procedures. Let us create a Stored procedure for the database access required for our login page and see what is the right way of doing the database operation using stored procedure.

CREATE PROCEDURE dbo.CheckUser     
      (
      @userID varchar(20),
      @password varchar(16)
      )
AS
      select userID from Users where userID = @userID and password = @password
      RETURN

And now lets have a good version in our code using this stored procedure.

public bool IsUserAuthenticated_Good(string username, string password)
{
    DataTable result = null;
    try
    {
        using (SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["SampleDbConnectionString1"].ConnectionString))
        {
            using (SqlCommand cmd = con.CreateCommand())
            {
                cmd.CommandType = CommandType.StoredProcedure;
                cmd.CommandText = "CheckUser";
                cmd.Parameters.Add(new SqlParameter("@userID", username));
                cmd.Parameters.Add(new SqlParameter("@password", password));

                using (SqlDataAdapter da = new SqlDataAdapter(cmd))
                {
                    result = new DataTable();
                    da.Fill(result);

                    //check if any match is found
                    if (result.Rows.Count == 1)
                    {
                        // return true to indicate that userID and password are matched.
                        return true;
                    }
                }
            }
        }
    }
    catch (Exception ex)
    {
        //Pokemon exception handling
    }

    //user id not found, lets treat him as a guest       
    return false;
}

If dynamic SQL is needed it should be used with parametrized commands.

If we still find our self needing the dynamic SQL in code then parametrized commands are the best way of performing such dynamic SQL business. This way we can always be sure of that no bad SQL is being generated. Let us create a parametrized command for the database access required for our Product page and see what is the right way of doing the database operation.

public DataTable GetProductsAssigner_Good(string userID)
{
    DataTable result = null;
    try
    {
        using (SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["SampleDbConnectionString1"].ConnectionString))
        {
            using (SqlCommand cmd = con.CreateCommand())
            {
                cmd.CommandType = CommandType.Text;
                cmd.CommandText = "select * from Products where AssignedTo = @userID";
                cmd.Parameters.Add(new SqlParameter("@userID", userID));

                using (SqlDataAdapter da = new SqlDataAdapter(cmd))
                {
                    result = new DataTable();
                    da.Fill(result);
                }
            }
        }
    }
    catch (Exception ex)
    {
        //Pokemon exception handling
    }

    //user id not found, lets treat him as a guest       
    return result;
}

All sensitive and confidential information should be stored in encrypted.

All the sensitive information should be stored encrypted in the database. The benefit of having this is that even if somehow the user get hold of the data he will only be able to see the encrypted values which are not easy to use for someone who doesn't know the encryption technique used by the application.

The application should never use/access the DB with Administrator privileges.

This will make sure that even if the bad SQL is being passed to the Database by some injections, the database will not allow any catastrophic actions like dropping table.

Note: Refer the sample application attached to see the working examples SQL injection and how to curb them using parametrized commands and stored procedures.



European SQL Hosting - Amsterdam :: Combine Multiple Columns And Records In MS SQL Server

clock May 20, 2013 11:55 by author Scott

In this example i am going to describe how to combine multiple columns and records in one column in MS SQL.

Here is the scenario

I have a table having Employees names and their respective Department names,
now i want to show Employees names separated by comma into one column and respective Department name in another column.

My table schema is shown in the image below

And this is Data into table

I want output in following format

                                  Department                               FirstName
                                   IT                                             amiT,Emp1,Emp5
                                  Admin                                       Shobhit, Emp3,Emp7

and so on

To get this desired result we need to write below mentioned query

1SELECT DISTINCT
2Department,
3EmpNames = substring( ( SELECT ', ' + FirstName
4FROM Employees e2
5WHERE e2.Department = e1.Department FOR XML path(''), elements
6),2,500)
7FROM Employees e1

And the output of this SQL Query would be



European SQL Hosting - Amsterdam :: Things to Consider While Restore Your Database

clock May 2, 2013 10:21 by author Scott

Here are some important points to consider while restoring a database backup. Let us first create a sample database named test using the following code.

A new database named test will be created in your server and data and log files are created in the d: drive.

Let us assume that you regularly take backup of this database using the below code:

backup database test to disk='d:\test.bak'

Now if you want to create another database or restore this test database to a new database named testing, you can use the following code

restore database testing from disk='d:\test.bak'

However executing the code above will give you the following error

Msg 1834, Level 16, State 1, Line 2
The file 'h:\test_dat.mdf' cannot be overwritten.  It is being used by database 'test'.
Msg 3156, Level 16, State 4, Line 2
File 'test_dat' cannot be restored to 'h:\test_dat.mdf'. Use WITH MOVE to identify a valid location for the file.
Msg 1834, Level 16, State 1, Line 2
The file 'h:\test_log.ldf' cannot be overwritten.  It is being used by database 'test'.
Msg 3156, Level 16, State 4, Line 2
File 'test_log' cannot be restored to 'h:\test_log.ldf'. Use WITH MOVE to identify a valid location for the file.
Msg 3119, Level 16, State 1, Line 2
Problems were identified while planning for the RESTORE statement. Previous messages provide details.
Msg 3013, Level 16, State 1, Line 2
RESTORE DATABASE is terminating abnormally.

This error occurs because the data and log files are currently being used by the database test. So you need to give different names for those files while restoring, as shown below

restore database testing from disk='d:\test.bak'
with
move 'test_dat' to 'd:\testing.mdf',
move 'test_log' to 'd:\testing.ldf'


The above code will work fine and new database will be created with the name testing.

Just be aware of this point while restoring a backup of existing database!

 



European SQL 2012 Hosting - Amsterdam :: Tabular Models vs PowerPivot Models SQL 2012

clock January 23, 2013 06:32 by author Scott

In SQL Server 2012, there is a new data model, called tabular, that is part of the new feature called the Business Intelligence Semantic Model (BISM).  BISM also includes the multidimensional model (formally called the UDM).

The Tabular model is based on concepts like tables and relationships that are familiar to anyone who has a relational database background, making it easier to use than the multidimensional model.  The tabular model is a server mode you choose when installing Analysis Services.

The tabular model is an enhancement of the current PowerPivot data model experience, both of which use the Vertipaq engine.  When opening a PowerPivot for SharePoint workbook, a SSAS cube is created behind the scenes, which is why PowerPivot for SharePoint requires SSAS to be installed.

So if tabular models and PowerPivot models use the same Analysis Services engine, why are tabular models necessary when we already have PowerPivot?

There are four things that tabular models offer that PowerPivot models does not:

  1. Scalability - PowerPivot has a 2 GB limit for the size of the Excel file and does not support partitions, but tabular model have no limit and support partitions.  Tabular models also support DirectQuery
  2. Manageability – There are a lot of tools you can use with the tabular model that you can’t use with PowerPivot: SSMS, AMO, AMOMD, XMLA, Deployment Wizard, AMO for PowerShell, and Integration Services
  3. Securability – Tabular models can use row security and dynamic security, neither of which PowerPivot supports, only Excel workbook file security
  4. Professional development toolchain - Tabular models live in the Visual Studio shell.  Thus, they enjoy all the shell services such as integrated source control, msbuild integration, and Team Build integration.  PowerPivot lives in the Excel environment, thus it is limited to the extensibility model provided in Excel (which doesn’t include source control or build configuration).  Also, because tabular models live in the VS environment, build and deployment can be naturally separated


So Analysis Services can now be installed in one of three server modes: Multidimensional and Data Mining (default), PowerPivot for SharePoint, and Tabular.

More info:

When to choose tabular models over PowerPivot models

Comparing Analysis Services and PowerPivot

Feature by Server Mode or Solution Type (SSAS)

 



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