technoblog

how to enable xp cmdshell in SQL 2005

2009-05-20T16:03:00.001-07:00

http://www.sql-server-performance.com/faq/enable_xp-cmdshell_2005_p1.aspx

SSIS Best Practices Link

2009-05-14T08:32:00.000-07:00

http://geekswithblogs.net/darrengosbell/archive/2007/10/21/SSIS-Best-Practices---SQL-Down-Under-Code-Camp-2007.aspx

Administer SQL Server remotely with VBScript/ASP

2009-05-13T19:21:00.001-07:00

Administer SQL Server remotely
By S.S. Ahmed

This article shows how to create tasks in the SQL Server remotely. VBScript, VB 6Win2K, WinXP, Visual Studio, Dev
Posted: 5 Nov 2001
Views: 72,732
Bookmarked: 23 times
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Download source files - 12.2 Kb
Download demo project - 3.84 Kb

Introduction

Before starting, let's shed some light on the SQL Distributed Management Objects (SQL-DMO). ASP gets its functionality by using server components. In ASP, we can combine scripts, HTML and reusable server components to create scalable web applications. These server-side ActiveX components can be developed in many languages, such as VC++, Java, and Visual Basic (VB).

I have selected VB to develop a component that will be used in ASP scripts to harness the power of SQL-DMO. SQL-DMOs are OLE automation-compatible COM objects. These objects and a set of properties and methods are used to write programs to administer multiple SQL Servers distributed across a network. Also, SQL-DMO is the foundation of SQL Enterprise Manager. In fact, SQL-DMO is a very powerful object model of SQL Server management. The obvious advantage of using a component encompassing SQL-DMO functionality is that you can manage your SQL Server from anywhere in the world.

Although, SQL-DMO is a complete set of objects and methods to manage the SQL Server remotely, in this article, we will only see how to add and remove SQL tasks in the Task Scheduler. I decided to write this article because I couldn't find a good article about using SQL-DMO in ASP. The article, which details how to leverage VB to create the ASP component, uses the following technologies:

Visual Basic 6
SQL Server
The Real Business

I have created a class named Task that contains all the code needed to implement the functionality.

This is the code from Task.cls:

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Public Function AddTask()

...........................

objSQLServer.DisConnect

objSQLServer.Connect Server, UserID, Password

Dim objTask As SQLOLE.Task
Set objTask = CreateObject("SQLOLE.Task")

'Set the schedule name

objTask.Name = TaskName

objSQLServer.Executive.Tasks.Add objTask

.................................

Case "single_run":
Case 2:

If ExecutionDate = "" Then
ErrDesc = "You must provide the task execution date."
Exit Function
Else
If IsDate(ExecutionDate) = False Then
ErrDesc = "Please provide a valid task execution date."
Exit Function
Else
'Set the schedule name

objTask.Name = TaskName

objSQLServer.Executive.Tasks.Add objTask

'Change the task!

objTask.BeginAlter
objTask.Database = DatabaseName
objTask.Command = CommandText

objTask.FrequencyType = SQLOLEFreq_OneTime
objTask.ActiveStartDate = CDate(ExecutionDate)
objTask.DoAlter
End If
End If

If (objTask.CmdExecSuccessCode) Then
ErrDesc = "Failure"
Else
ErrDesc = "Success"
End If

End Function
The class has two main functions named AddTask and RemoveTask. AddTask adds a new task to the Scheduler. Similarly, RemoveTask removes the task from the Scheduler. First of all, you will have to include the "Microsoft SQL OLE Object library" from the references in the Project menu. Once you have done that, follow the steps below:

Create a SQL Server object.
Connect to the SQL Server object.
Use the SQL Server object and other contained objects.
Release the SQL Server object.
Step 1

The following creates a new SQL Server object:

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Dim objSQLServer As SQLOLE.SQLServer
Set objSQLServer = New SQLOLE.SQLServer
The objSQLServer object is an instance of the SQLOLE.SQLServer class. This object represents the SQL Server in which tasks will be added or removed. It's needed in order to move ahead and create another object that will be used to create a new task. Notice that this uses the New keyword to instantiate the SQLServer object. We could have used the CreateObject function instead, but late binding would have given the app a slower performance. The reference through an early bound variable promotes a better performance.

Step 2

The following connects to the SQLServer object:

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objSQLServer.Connect Server, UserID, Password
Note that we have passed three arguments to the Connect method. The first argument is the name of the SQL Server to which you want to connect, the second argument is the User ID required to log on to the SQL Server, and the third argument is the password required to log on to the SQL Server. If you provide correct parameters to the Connect method, you will be connected to the SQL Server.

Step 3

Once you are connected to the SQL Server, you can make use of the newly created object's methods and properties to accomplish the task. Our task is to create a new task in the SQL Scheduler. So we are going to create a new task, and later we will set certain properties of this object.

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Dim objTask As SQLOLE.Task
Set objTask = CreateObject("SQLOLE.Task")
Now that the task object has been created, we need to add the task to the scheduler. Define the task name by calling the Name property of the Task object, and then add this task to the SQL Server Scheduler.

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objTask.Name = TaskName
objSQLServer.Executive.Tasks.Add objTask
After the task has been added to the Scheduler, it's time to add some commands in the newly created task. You may want to create and run a task to delete particular records from a table at a particular time, or you may want to send an email to the site administrator on an exact date of the month. All of this can be done by assigning values to certain properties of the Task object. Look at the following statements:

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objTask.BeginAlter
objTask.Database = DatabaseName
objTask.Command = CommandText

objTask.FrequencyType = SQLOLEFreq_OneTime
objTask.ActiveStartDate = CDate(ExecutionDate)
objTask.DoAlter
Before assigning values to the properties, you must call BeginAlter method, which tells the SQL Server that changes are about to be made to the task properties. Actually, each change to a single property is a separate update to SQL Server. We use the BeginAlter method to group multiple property changes into a single unit. Call the DoAlter method to commit the changes made to the object properties. You can also call the CancelAlter method to cancel the unit of property changes.

Assign a valid database name to the Database property. This is the database in which you want to execute the task.

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objTask.Database = DatabaseName
Pass a valid Transact SQL statement to execute the task you have created, to the Command property.

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objTask.Command = CommandText
In the original Task code, we assigned a valid value to the FrequencyType property, which is the primary frequency unit of time. More details are included in the source code files accompanying this article. Please refer to the component's source code to see the different uses of the FrequencyType property.

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objTask.FrequencyType = SQLOLEFreq_OneTime
The above line of code is meant to run only once, therefore a date is assigned to the ActiveStartDate property. The task will automatically execute on this date. ActiveStartDate is the date before which this task is active. There is another property which I think should be mentioned here, ActiveEndDate, the date and time after which the task is active.

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objTask.ActiveStartDate = CDate(ExecutionDate)
Using the code provided, you could create a task that would run on a daily basis, hourly basis, or only once on the date provided as a parameter. By viewing the attached source code in Visual Basic, a reader can see that it is thoroughly commented, so the reader can understand the statements without frequently pressing F1 to discover a statement's meaning. The following is the RemoveTask function that removes the named task from the scheduler:

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Public Function RemoveTask(ByVal Task As Variant)

..........................

objSQLServer.Connect Server, UserID, Password

objSQLServer.Executive.Tasks(CStr(Task)).Remove
ErrDesc = "The task has been removed."

.........................

End Function
Remember, it's necessary to set certain properties before calling this method. Have a look at the following statements:

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Dim objTaskManager
Set objTaskManger = server.createobject("TaskManager.Task")

objTaskManager.Server = cstr(request.form("servername"))
objTaskManager.UserID = cstr(request.form("userid"))
objTaskManager.Password = cstr(request.form("password"))
objTaskManager.RemoveTask cstr(request.form("taskname"))

response.write objTaskManager.ErrDesc

Set objTaskManager = Nothing
This is the ASP code that shows how to instantiate the component and call the RemoveTask function. Notice that before the function is called, server name, user ID, and password values are passed to the properties. Use the ErrDesc property to see the status of the function called.

Following is the ASP code needed to add a new task to the SQL Scheduler:

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Dim objTaskManager
Set objTaskManager = server.createobject("TaskManager.Task")

objTaskManager.Server = cstr(request.form("servername"))
objTaskManager.UserID = cstr(request.form("userid"))
objTaskManager.Password = cstr(request.form("password"))
objTaskManager.DatabaseName = cstr(request.form("databasename"))
objTaskManager.TaskName = cstr(request.form("taskname"))
objTaskManager.CommandText = cstr(request.form("commandtext"))
objTaskManager.ScheduleType = cint(request.form("scheduletype"))
objTaskManager.ExecutionDate = cstr(request.form("executiondate"))
objTaskManager.AddTask

response.write objTaskManager.ErrDesc
Set objTaskManager = Nothing
The task created above will run only once because we have passed the current date to the ExecutionDate property.

Compiling the Project

After entering the code in the class module, compile the project to make a DLL. It would be better to reference the "Microsoft Active Server Pages Object Library" in the project, so ASP will not give us an "Out of Process Component" error message if we try to call the component from any ASP page. In a nutshell, what this means is that this component will know that it needs to access the Active Server Pages DLL (asp.dll) to run. Finally, compile the project as a DLL. Voila! You have created an ASP component that can add and remove SQL Scheduler tasks.

Usage

Consider a scenario in which you create an e-commerce application. You have used SQL Server for data-storage purposes. Users come and register on your site before doing any shopping on your site, and they place orders, but leave your site without checking out.

You should be able to delete the items they placed in their shopping basket. It would be tedious to manually check the database for valid records and delete the unwanted records. Instead, use the component you just created and create a task that would search the database for invalid or unwanted records and would delete them automatically after a certain amount of time.

Similarly, you can create and run a VB application once a month that would remove the accomplished tasks from the SQL Server. Alternately, you could create a component that would check and remove the unwanted tasks from the SQL Server, create a new task manually, and call this component using the extended stored procedures provided with SQL Server to remove the unwanted tasks from the SQL Server. SQL Server 6.5 and later provides the capability of loading and executing COM objects through a set of OLE Automation stored procedures or through extended stored procedures.

Code Details

VB component source code and ASP files to test the component are provided with this article. A compiled DLL is also provided. Directly plug in the DLL in your web application to test the component functionality. Source code is also provided so that you can play with the code yourself and try to add some more features in the component. ASP files are provided to test the component in ASP. Create and remove tasks through these files. To run the ASP files, create a new web application and include all the ASP files in the new application, and open the index file, tm_demo1.asp, in your browser to test the functionality.

Summary

Creating ASP Component to manage SQL Server remotely is fairly easy. It only requires a basic knowledge of ASP, VB and SQL Server. The article shows how easy it is to create a component that harnesses the power of SQL-DMO and manages the SQL tasks remotely.

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here

RSS Feed Code Page

2009-05-13T15:37:00.001-07:00

http://www.codeproject.com/KB/smart/rssfeeder.aspx

ASP Questions

2009-05-13T09:05:00.000-07:00

* From constructor to destructor (taking into consideration Dispose() and the concept of non-deterministic finalization), what the are events fired as part of the ASP.NET System.Web.UI.Page lifecycle. Why are they important? What interesting things can you do at each?
* What are ASHX files? What are HttpHandlers? Where can they be configured?
* What is needed to configure a new extension for use in ASP.NET? For example, what if I wanted my system to serve ASPX files with a *.jsp extension?
* What events fire when binding data to a data grid? What are they good for?
* Explain how PostBacks work, on both the client-side and server-side. How do I chain my own JavaScript into the client side without losing PostBack functionality?
* How does ViewState work and why is it either useful or evil?
* What is the OO relationship between an ASPX page and its CS/VB code behind file in ASP.NET 1.1? in 2.0?
* What happens from the point an HTTP request is received on a TCP/IP port up until the Page fires the On_Load event?
* How does IIS communicate at runtime with ASP.NET? Where is ASP.NET at runtime in IIS5? IIS6?
* What is an assembly binding redirect? Where are the places an administrator or developer can affect how assembly binding policy is applied?
* Compare and contrast LoadLibrary(), CoCreateInstance(), CreateObject() and Assembly.Load().

.NET WebDev interview questions - Part 3
By admin | February 4, 2006

1. State True or False: If you set AutoGenerateColumns=True and still provide custom column definitions, the DataGrid will render both
* True
* False
2. The data from an XSL Transform with XmlReader can be returned in one of the following ways
* objReader = objXslT.Transform(objNav, nothing)
* objXslT.Transform(objNav, nothing)
* objReader = objXslT.Transform(objNav, nothing, objWriter)
* objXslT.Transform(objNav, nothing, objWriter)
3. Pick the command line that would result in the C# compiler generating an XML documentation file
* csc /doc:NewHome.xml NewHome.cs
* c /doc /docfile: NewHome.xml NewHome.cs
* csc /doc /out: NewHome.xml NewHome.cs
* csc /xml NewHome.cs
4. What is the comment syntax for C#’s XML-based documentation?
* /** and **/
* //#
* ///
* //*

5. When creating a C# Class Library project, what is the name of the supplementary file that Visual Studio.NET creates that contains General Information about the assembly?
* AssemblyInfo.xml
* AssemblyInfo.cs
* AssemblyInformation.cs
* AssemblyAttributes.cs
6. Which of the following is the C# escape character for Null?
* \n
* \0
* \f
* \v
7. What is the exception that is thrown when there is an attempt to dynamically access a method that does not exist?
* MissingMethodException
* TypeLoadException
* MethodLoadException
* MethodAccessException
8. What method(s) must be used with the Application object to ensure that only one process accesses a variable at a time?
* Synchronize()
* Lock() and UnLock()
* Lock()
* Asynchroize()
9. After capturing the SelectedIndexChanged event for a ListBox control, you find that the event handler doesn’t execute. What could the problem be?
* The AutoEventWireup attribute is set to False
* The AutomaticPostBack attribute is set to False
* The codebehind module is not properly compiled
* The ListBox must be defined WithEvents
10. What method must be overridden in a custom control?
* The Paint() method
* The Control_Build() method
* The Render() method
* The default constructor
11. What is used to validate complex string patterns like an e-mail address?
* Extended expressions
* Regular expressions
* Irregular expressions
* Basic expressions
12. The following is a valid statement in ASP.NET<%@ Page Language="C" %>
* True
* False
13. A valid comment block in ASP.NET is
*
*
* <% - - Comment - - %>
* <% ! - - Comment - - >
14. The event handlers that can be included in the Global.asax file are
* Application Start and
Session Start event handlers only
* Application End and
Session End event handlers only
* Per-request and Non-deterministic event handlers only
* Application Start and End ,
Session Start and End, Per-request and Non-deterministic event handlers
15. A Few of the Namespaces that get imported by default in an ASPX file are
* System, System.Data, System.Drawing,
System.Globalization
* System,
System.IO, System.Management, System.Globalization
* System, System.Collections,
System.Text, System.Web
* System,
System.NET,
System.Reflection, System.Web
16. The Assemblies that can be referenced in an ASPX file without using @Assembly Directive is
* System.dll, System.Data.dll,
System.Web.dll, System.Xml.dll,
* System.dll,
System.Collections.dll, System.IO.dll
* System.dll, System.Reflection.dll,
System.Globalization.dll,
* System.Drawing.dll, System.Assembly.dll,
System.Text.dll
17. An .ASHX file contains the following
* Code-behind that are used in the code
* Server Controls that can be called from a code-behind file
* HTTP handlers-software modules that handle raw HTTP requests received by ASP.NET
* Contains normal ASP.NET code and can be used as an include file
18. What is the output for the following code snippet:

public class testClass
{
public static void Main(string[] args)
{
System.Console.WriteLine(args[1]);
}//end Main
}//end class testClass

* Compiler Error
* Runtime Error
* Hello C# world
* None of the above
19. One of the possible way of writing an ASP.NET handler that works like an ISAPI filter- that is, that sees requests and responses and modifies them also, is by,
* writing a module that extends FormsAuthenticatonModule and using it
* writing a component class that extends HttpModuleCollection and using it
* writing an HTTP module-a Class that implements IhttpModule and registering it in Web.Config
* All of the above
20. The ASP.NET directive that lets you cache different versions of a page based on varying input parameters, HTTP headers and browser type is
* @OutputCache
* @CacheOutput
* @PageCache
* @CacheAll
21. If we develop an application that must accommodate multiple security levels through secure login and ASP.NET web application is spanned across three web-servers (using round-robin load balancing) what would be the best approach to maintain login-in state for the users?
*
*
*
22. What is the output for the below mentioned compilation command>csc /addmodule:A.Exe B.Cs
* A.exe
* B.exe
* A.dll
* B.dll
23. How can be the web application get configured with the following authorization rules
* Anonymous users must not be allowed to access the application.
* All persons except David and John must be allowed to access the application.
o
o
o
o

24. What will be the output of the following code snippet?

using System;
class MainClass
{
static void Main( )
{
new MainClass().Display( 3.56 );
}

private void Display( float anArg )
{
Console.Write( "{0} {1}", anArg.GetType(), anArg );
}

double Display( double anArg )
{
Console.Write( "{0} {1}", anArg.GetType(), anArg );
return anArg;
}

public decimal Display( decimal anArg )
{
Console.Write( "{0} {1}", anArg.GetType(), anArg ); return anArg;
}
}

* System.Single 3.56

* System.Float 3.56

* System.Double 3.56

* System.Decimal 3.56
25. What will be output for the given code?

Dim I as integer = 5
Do
I = I + 2
Response.Write (I & " ")
Loop Until I > 10

* 5 8

* 5 7 9

* 7 9 11

* Errors out

SQL Server Interview Questions/Answers

2009-05-13T07:10:00.000-07:00

Here are some SQL Server DBA/Developer interview questions I faced myself personally and/or heard from people. I will try to answer these questions briefly here, but be advised that these answers may not be complete and it will be better for you to go through text books, books online and other resources on the net. At the end of this article, I listed some useful books for aspiring DBAs and developers.

Before you go for the interview, be prepared to explain the database design of one of your latest projects. Don't be surprised if the interviewer asks you to draw ER diagrams.

Well, here are some questions for you. Hope this helps you prepare for your interview. Wish you all the best in your job hunt! Feel free to email me 'interview questions' that you've faced.

Questions are categorized under the following sections, for your convenience:

Database design	(8 questions)
SQL Server architecture	(12 questions)
Database administration	(13 questions)
Database programming	(10 questions)

Database design

(top)

What is normalization? Explain different levels of normalization?

Check out the article Q100139 from Microsoft knowledge base and of course, there's much more information available in the net. It'll be a good idea to get a hold of any RDBMS fundamentals text book, especially the one by C. J. Date. Most of the times, it will be okay if you can explain till third normal form.

What is denormalization and when would you go for it?

As the name indicates, denormalization is the reverse process of normalization. It's the controlled introduction of redundancy in to the database design. It helps improve the query performance as the number of joins could be reduced.

How do you implement one-to-one, one-to-many and many-to-many relationships while designing tables?

One-to-One relationship can be implemented as a single table and rarely as two tables with primary and foreign key relationships.
One-to-Many relationships are implemented by splitting the data into two tables with primary key and foreign key relationships.
Many-to-Many relationships are implemented using a junction table with the keys from both the tables forming the composite primary key of the junction table.

It will be a good idea to read up a database designing fundamentals text book.

What's the difference between a primary key and a unique key?

Both primary key and unique enforce uniqueness of the column on which they are defined. But by default primary key creates a clustered index on the column, where are unique creates a nonclustered index by default. Another major difference is that, primary key doesn't allow NULLs, but unique key allows one NULL only.

What are user defined datatypes and when you should go for them?

User defined datatypes let you extend the base SQL Server datatypes by providing a descriptive name, and format to the database. Take for example, in your database, there is a column called Flight_Num which appears in many tables. In all these tables it should be varchar(8). In this case you could create a user defined datatype called Flight_num_type of varchar(8) and use it across all your tables.

See sp_addtype, sp_droptype in books online.

What is bit datatype and what's the information that can be stored inside a bit column?

Bit datatype is used to store boolean information like 1 or 0 (true or false). Untill SQL Server 6.5 bit datatype could hold either a 1 or 0 and there was no support for NULL. But from SQL Server 7.0 onwards, bit datatype can represent a third state, which is NULL.

Define candidate key, alternate key, composite key.

A candidate key is one that can identify each row of a table uniquely. Generally a candidate key becomes the primary key of the table. If the table has more than one candidate key, one of them will become the primary key, and the rest are called alternate keys.

A key formed by combining at least two or more columns is called composite key.

What are defaults? Is there a column to which a default can't be bound?

A default is a value that will be used by a column, if no value is supplied to that column while inserting data. IDENTITY columns and timestamp columns can't have defaults bound to them. See CREATE DEFUALT in books online.

SQL Server architecture

(top)

What is a transaction and what are ACID properties?

A transaction is a logical unit of work in which, all the steps must be performed or none. ACID stands for Atomicity, Consistency, Isolation, Durability. These are the properties of a transaction. For more information and explanation of these properties, see SQL Server books online or any RDBMS fundamentals text book.

Explain different isolation levels

An isolation level determines the degree of isolation of data between concurrent transactions. The default SQL Server isolation level is Read Committed. Here are the other isolation levels (in the ascending order of isolation): Read Uncommitted, Read Committed, Repeatable Read, Serializable. See SQL Server books online for an explanation of the isolation levels. Be sure to read about SET TRANSACTION ISOLATION LEVEL, which lets you customize the isolation level at the connection level.

CREATE INDEX myIndex ON myTable(myColumn)

What type of Index will get created after executing the above statement?

Non-clustered index. Important thing to note: By default a clustered index gets created on the primary key, unless specified otherwise.

What's the maximum size of a row?

8060 bytes. Don't be surprised with questions like 'what is the maximum number of columns per table'. Check out SQL Server books online for the page titled: "Maximum Capacity Specifications".

Explain Active/Active and Active/Passive cluster configurations

Hopefully you have experience setting up cluster servers. But if you don't, at least be familiar with the way clustering works and the two clusterning configurations Active/Active and Active/Passive. SQL Server books online has enough information on this topic and there is a good white paper available on Microsoft site.

Explain the architecture of SQL Server

This is a very important question and you better be able to answer it if consider yourself a DBA. SQL Server books online is the best place to read about SQL Server architecture. Read up the chapter dedicated to SQL Server Architecture.

What is lock escalation?

Lock escalation is the process of converting a lot of low level locks (like row locks, page locks) into higher level locks (like table locks). Every lock is a memory structure too many locks would mean, more memory being occupied by locks. To prevent this from happening, SQL Server escalates the many fine-grain locks to fewer coarse-grain locks. Lock escalation threshold was definable in SQL Server 6.5, but from SQL Server 7.0 onwards it's dynamically managed by SQL Server.

What's the difference between DELETE TABLE and TRUNCATE TABLE commands?

DELETE TABLE is a logged operation, so the deletion of each row gets logged in the transaction log, which makes it slow. TRUNCATE TABLE also deletes all the rows in a table, but it won't log the deletion of each row, instead it logs the deallocation of the data pages of the table, which makes it faster. Of course, TRUNCATE TABLE can be rolled back.

Explain the storage models of OLAP

Check out MOLAP, ROLAP and HOLAP in SQL Server books online for more infomation.

What are the new features introduced in SQL Server 2000 (or the latest release of SQL Server at the time of your interview)? What changed between the previous version of SQL Server and the current version?

This question is generally asked to see how current is your knowledge. Generally there is a section in the beginning of the books online titled "What's New", which has all such information. Of course, reading just that is not enough, you should have tried those things to better answer the questions. Also check out the section titled "Backward Compatibility" in books online which talks about the changes that have taken place in the new version.

What are constraints? Explain different types of constraints.

Constraints enable the RDBMS enforce the integrity of the database automatically, without needing you to create triggers, rule or defaults.

Types of constraints: NOT NULL, CHECK, UNIQUE, PRIMARY KEY, FOREIGN KEY

For an explanation of these constraints see books online for the pages titled: "Constraints" and "CREATE TABLE", "ALTER TABLE"

Whar is an index? What are the types of indexes? How many clustered indexes can be created on a table? I create a separate index on each column of a table. what are the advantages and disadvantages of this approach?

Indexes in SQL Server are similar to the indexes in books. They help SQL Server retrieve the data quicker.

Indexes are of two types. Clustered indexes and non-clustered indexes. When you craete a clustered index on a table, all the rows in the table are stored in the order of the clustered index key. So, there can be only one clustered index per table. Non-clustered indexes have their own storage separate from the table data storage. Non-clustered indexes are stored as B-tree structures (so do clustered indexes), with the leaf level nodes having the index key and it's row locater. The row located could be the RID or the Clustered index key, depending up on the absence or presence of clustered index on the table.

If you create an index on each column of a table, it improves the query performance, as the query optimizer can choose from all the existing indexes to come up with an efficient execution plan. At the same t ime, data modification operations (such as INSERT, UPDATE, DELETE) will become slow, as every time data changes in the table, all the indexes need to be updated. Another disadvantage is that, indexes need disk space, the more indexes you have, more disk space is used.

Database administration

(top)

What is RAID and what are different types of RAID configurations?

RAID stands for Redundant Array of Inexpensive Disks, used to provide fault tolerance to database servers. There are six RAID levels 0 through 5 offering different levels of performance, fault tolerance. MSDN has some information about RAID levels and for detailed information, check out the RAID advisory board's homepage

What are the steps you will take to improve performance of a poor performing query?

This is a very open ended question and there could be a lot of reasons behind the poor performance of a query. But some general issues that you could talk about would be: No indexes, table scans, missing or out of date statistics, blocking, excess recompilations of stored procedures, procedures and triggers without SET NOCOUNT ON, poorly written query with unnecessarily complicated joins, too much normalization, excess usage of cursors and temporary tables.

Some of the tools/ways that help you troubleshooting performance problems are: SET SHOWPLAN_ALL ON, SET SHOWPLAN_TEXT ON, SET STATISTICS IO ON, SQL Server Profiler, Windows NT /2000 Performance monitor, Graphical execution plan in Query Analyzer.

Download the white paper on performance tuning SQL Server from Microsoft web site. Don't forget to check out sql-server-performance.com

What are the steps you will take, if you are tasked with securing an SQL Server?

Again this is another open ended question. Here are some things you could talk about: Preferring NT authentication, using server, databse and application roles to control access to the data, securing the physical database files using NTFS permissions, using an unguessable SA password, restricting physical access to the SQL Server, renaming the Administrator account on the SQL Server computer, disabling the Guest account, enabling auditing, using multiprotocol encryption, setting up SSL, setting up firewalls, isolating SQL Server from the web server etc.

Read the white paper on SQL Server security from Microsoft website. Also check out My SQL Server security best practices

What is a deadlock and what is a live lock? How will you go about resolving deadlocks?

Deadlock is a situation when two processes, each having a lock on one piece of data, attempt to acquire a lock on the other's piece. Each process would wait indefinitely for the other to release the lock, unless one of the user processes is terminated. SQL Server detects deadlocks and terminates one user's process.

A livelock is one, where a request for an exclusive lock is repeatedly denied because a series of overlapping shared locks keeps interfering. SQL Server detects the situation after four denials and refuses further shared locks. A livelock also occurs when read transactions monopolize a table or page, forcing a write transaction to wait indefinitely.

Check out SET DEADLOCK_PRIORITY and "Minimizing Deadlocks" in SQL Server books online. Also check out the article Q169960 from Microsoft knowledge base.

What is blocking and how would you troubleshoot it?

Blocking happens when one connection from an application holds a lock and a second connection requires a conflicting lock type. This forces the second connection to wait, blocked on the first.

Read up the following topics in SQL Server books online: Understanding and avoiding blocking, Coding efficient transactions.

Explain CREATE DATABASE syntax

Many of us are used to craeting databases from the Enterprise Manager or by just issuing the command: CREATE DATABAE MyDB. But what if you have to create a database with two filegroups, one on drive C and the other on drive D with log on drive E with an initial size of 600 MB and with a growth factor of 15%? That's why being a DBA you should be familiar with the CREATE DATABASE syntax. Check out SQL Server books online for more information.

How to restart SQL Server in single user mode? How to start SQL Server in minimal configuration mode?

SQL Server can be started from command line, using the SQLSERVR.EXE. This EXE has some very important parameters with which a DBA should be familiar with. -m is used for starting SQL Server in single user mode and -f is used to start the SQL Server in minimal confuguration mode. Check out SQL Server books online for more parameters and their explanations.

As a part of your job, what are the DBCC commands that you commonly use for database maintenance?

DBCC CHECKDB, DBCC CHECKTABLE, DBCC CHECKCATALOG, DBCC CHECKALLOC, DBCC SHOWCONTIG, DBCC SHRINKDATABASE, DBCC SHRINKFILE etc. But there are a whole load of DBCC commands which are very useful for DBAs. Check out SQL Server books online for more information.

What are statistics, under what circumstances they go out of date, how do you update them?

Statistics determine the selectivity of the indexes. If an indexed column has unique values then the selectivity of that index is more, as opposed to an index with non-unique values. Query optimizer uses these indexes in determining whether to choose an index or not while executing a query.

Some situations under which you should update statistics:
1) If there is significant change in the key values in the index
2) If a large amount of data in an indexed column has been added, changed, or removed (that is, if the distribution of key values has changed), or the table has been truncated using the TRUNCATE TABLE statement and then repopulated
3) Database is upgraded from a previous version

Look up SQL Server books online for the following commands: UPDATE STATISTICS, STATS_DATE, DBCC SHOW_STATISTICS, CREATE STATISTICS, DROP STATISTICS, sp_autostats, sp_createstats, sp_updatestats

What are the different ways of moving data/databases between servers and databases in SQL Server?

There are lots of options available, you have to choose your option depending upon your requirements. Some of the options you have are: BACKUP/RESTORE, dettaching and attaching databases, replication, DTS, BCP, logshipping, INSERT...SELECT, SELECT...INTO, creating INSERT scripts to generate data.

Explian different types of BACKUPs avaialabe in SQL Server? Given a particular scenario, how would you go about choosing a backup plan?

Types of backups you can create in SQL Sever 7.0+ are Full database backup, differential database backup, transaction log backup, filegroup backup. Check out the BACKUP and RESTORE commands in SQL Server books online. Be prepared to write the commands in your interview. Books online also has information on detailed backup/restore architecture and when one should go for a particular kind of backup.

What is database replicaion? What are the different types of replication you can set up in SQL Server?

Replication is the process of copying/moving data between databases on the same or different servers. SQL Server supports the following types of replication scenarios:

Snapshot replication
Transactional replication (with immediate updating subscribers, with queued updating subscribers)
Merge replication

See SQL Server books online for indepth coverage on replication. Be prepared to explain how different replication agents function, what are the main system tables used in replication etc.

How to determine the service pack currently installed on SQL Server?

The global variable @@Version stores the build number of the sqlservr.exe, which is used to determine the service pack installed. To know more about this process visit SQL Server service packs and versions.

Database programming

(top)

What are cursors? Explain different types of cursors. What are the disadvantages of cursors? How can you avoid cursors?

Cursors allow row-by-row prcessing of the resultsets.

Types of cursors: Static, Dynamic, Forward-only, Keyset-driven. See books online for more information.

Disadvantages of cursors: Each time you fetch a row from the cursor, it results in a network roundtrip, where as a normal SELECT query makes only one rowundtrip, however large the resultset is. Cursors are also costly because they require more resources and temporary storage (results in more IO operations). Furthere, there are restrictions on the SELECT statements that can be used with some types of cursors.

Most of the times, set based operations can be used instead of cursors. Here is an example:

If you have to give a flat hike to your employees using the following criteria:

Salary between 30000 and 40000 -- 5000 hike
Salary between 40000 and 55000 -- 7000 hike
Salary between 55000 and 65000 -- 9000 hike

In this situation many developers tend to use a cursor, determine each employee's salary and update his salary according to the above formula. But the same can be achieved by multiple update statements or can be combined in a single UPDATE statement as shown below:

UPDATE tbl_emp SET salary =
CASE WHEN salary BETWEEN 30000 AND 40000 THEN salary + 5000
WHEN salary BETWEEN 40000 AND 55000 THEN salary + 7000
WHEN salary BETWEEN 55000 AND 65000 THEN salary + 10000
END

Another situation in which developers tend to use cursors: You need to call a stored procedure when a column in a particular row meets certain condition. You don't have to use cursors for this. This can be achieved using WHILE loop, as long as there is a unique key to identify each row. For examples of using WHILE loop for row by row processing, check out the 'My code library' section of my site or search for WHILE.

Write down the general syntax for a SELECT statements covering all the options.

Here's the basic syntax: (Also checkout SELECT in books online for advanced syntax).

SELECT select_list
[INTO new_table_]
FROM table_source
[WHERE search_condition]
[GROUP BY group_by_expression]
[HAVING search_condition]
[ORDER BY order_expression [ASC | DESC] ]

What is a join and explain different types of joins.

Joins are used in queries to explain how different tables are related. Joins also let you select data from a table depending upon data from another table.

Types of joins: INNER JOINs, OUTER JOINs, CROSS JOINs. OUTER JOINs are further classified as LEFT OUTER JOINS, RIGHT OUTER JOINS and FULL OUTER JOINS.

For more information see pages from books online titled: "Join Fundamentals" and "Using Joins".

Can you have a nested transaction?

Yes, very much. Check out BEGIN TRAN, COMMIT, ROLLBACK, SAVE TRAN and @@TRANCOUNT

What is an extended stored procedure? Can you instantiate a COM object by using T-SQL?

An extended stored procedure is a function within a DLL (written in a programming language like C, C++ using Open Data Services (ODS) API) that can be called from T-SQL, just the way we call normal stored procedures using the EXEC statement. See books online to learn how to create extended stored procedures and how to add them to SQL Server.

Yes, you can instantiate a COM (written in languages like VB, VC++) object from T-SQL by using sp_OACreate stored procedure. Also see books online for sp_OAMethod, sp_OAGetProperty, sp_OASetProperty, sp_OADestroy. For an example of creating a COM object in VB and calling it from T-SQL, see 'My code library' section of this site.

What is the system function to get the current user's user id?

USER_ID(). Also check out other system functions like USER_NAME(), SYSTEM_USER, SESSION_USER, CURRENT_USER, USER, SUSER_SID(), HOST_NAME().

What are triggers? How many triggers you can have on a table? How to invoke a trigger on demand?

Triggers are special kind of stored procedures that get executed automatically when an INSERT, UPDATE or DELETE operation takes place on a table.

In SQL Server 6.5 you could define only 3 triggers per table, one for INSERT, one for UPDATE and one for DELETE. From SQL Server 7.0 onwards, this restriction is gone, and you could create multiple triggers per each action. But in 7.0 there's no way to control the order in which the triggers fire. In SQL Server 2000 you could specify which trigger fires first or fires last using sp_settriggerorder

Triggers can't be invoked on demand. They get triggered only when an associated action (INSERT, UPDATE, DELETE) happens on the table on which they are defined.

Triggers are generally used to implement business rules, auditing. Triggers can also be used to extend the referential integrity checks, but wherever possible, use constraints for this purpose, instead of triggers, as constraints are much faster.

Till SQL Server 7.0, triggers fire only after the data modification operation happens. So in a way, they are called post triggers. But in SQL Server 2000 you could create pre triggers also. Search SQL Server 2000 books online for INSTEAD OF triggers.

Also check out books online for 'inserted table', 'deleted table' and COLUMNS_UPDATED()

There is a trigger defined for INSERT operations on a table, in an OLTP system. The trigger is written to instantiate a COM object and pass the newly insterted rows to it for some custom processing. What do you think of this implementation? Can this be implemented better?

Instantiating COM objects is a time consuming process and since you are doing it from within a trigger, it slows down the data insertion process. Same is the case with sending emails from triggers. This scenario can be better implemented by logging all the necessary data into a separate table, and have a job which periodically checks this table and does the needful.

What is a self join? Explain it with an example.

Self join is just like any other join, except that two instances of the same table will be joined in the query. Here is an example: Employees table which contains rows for normal employees as well as managers. So, to find out the managers of all the employees, you need a self join.

CREATE TABLE emp
(
empid int,
mgrid int,
empname char(10)
)

INSERT emp SELECT 1,2,'Vyas'
INSERT emp SELECT 2,3,'Mohan'
INSERT emp SELECT 3,NULL,'Shobha'
INSERT emp SELECT 4,2,'Shridhar'
INSERT emp SELECT 5,2,'Sourabh'

SELECT t1.empname [Employee], t2.empname [Manager]
FROM emp t1, emp t2
WHERE t1.mgrid = t2.empid

Here's an advanced query using a LEFT OUTER JOIN that even returns the employees without managers (super bosses)

SELECT t1.empname [Employee], COALESCE(t2.empname, 'No manager') [Manager]
FROM emp t1
LEFT OUTER JOIN
emp t2
ON
t1.mgrid = t2.empid

Given an employee table, how would you find out the second highest salary?

For a solution see the 'My code library' section of this site.

duplicate removal cursor

2009-04-23T12:26:00.001-07:00

Create procedure spBLSfixdupesproductvariant as

DECLARE @cnt int, @custID as int

DECLARE dupCursor CURSOR FAST_FORWARD

FOR SELECT PV.ProductID, COUNT(PV.ProductID) AS Cnt

from aspdotnetstorefront8011.dbo.ProductVariant pv

join aspdotnetstorefront8011.dbo.product p

on pv.productid = p.productid

group by pv.productid, pv.createdon,cast(p.Extensiondata as varchar(40))

having count(pv.productid) > 1 and cast(p.Extensiondata as varchar(40))='BlueStar'

OPEN dupCursor

FETCH NEXT FROM dupCursor

INTO @custID, @cnt

WHILE @@FETCH_STATUS = 0

BEGIN

DELETE Top (@cnt-1)

FROM aspdotnetstorefront8011.dbo.ProductVariant

WHERE ProductID= @custID

FETCH NEXT FROM dupCursor

INTO @custID, @cnt

END

CLOSE dupCursor

DEALLOCATE dupCursor

get database objects information for all databases on SQL Server

2009-04-23T09:26:00.000-07:00

-- Part 1

Declare @sqlstr nvarchar(200)

-- Part 2

/* drop the temporary table if already exists */

If Object_Id('tempdb..#tblDBObjects') is Not Null

Drop table #tblDBObjects

/* create temporary table */

Create TABLE #tblDBObjects (

dbName sysname,

objName varchar(200),

objtype char(2),

objtypename varchar(200),

crdate datetime,

)

-- Part 3

/*assign string value to variable */

Select @sqlstr = 'sp_msforeachdb ''Insert #tblDBObjects select ''''?'''' as DBName, sysobjects.name, xtype,type_desc,crdate From ?..sysobjects join sys.objects on sysobjects.id=sys.objects.object_id'''

/* execute SQL string */

Exec sp_executesql @sqlstr

-- Part 4

/* select from temp table */

Select * From #tblDBObjects order by crdate desc

RETURN

Good SQL Comment Block to Use

2009-04-20T06:11:00.001-07:00

/*
----------------------------------------------------------------------------
-- Object Name:
-- Project:
-- Business Process:
-- Purpose:
-- Detailed Description:
-- Database:
-- Dependent Objects:
-- Called By:
-- Upstream Systems:
-- Downstream Systems:
--
--------------------------------------------------------------------------------------
-- Rev | CMR | Date Modified | Developer | Change Summary
--------------------------------------------------------------------------------------
-- | | | |
--
*/

SQL Server Pedia Knowledge Base link

2009-04-19T13:41:00.001-07:00

http://sqlserverpedia.com/wiki/Performance_Monitor

Microsoft Ramp Up link

2009-04-17T07:34:00.001-07:00

http://msdn.microsoft.com/en-us/rampup/dd425032.aspx

Full text population TSQL 2005

2009-04-16T08:28:00.001-07:00

This is a cursor based script from Microsoft to use for full text populations

-- Sample script to start full-text index population for
-- each full-text index.
create Procedure sp_STARTFULLTEXTPOPULATION as
DECLARE @table_name NVARCHAR(517),
@schema_name NVARCHAR(517);
DECLARE @exec_str NVARCHAR(4000);
DECLARE @change_tracking_state NCHAR(1);
-- Retrieve a list of tables with full-text indexes and start full
-- full-text index population for each full-text index.
DECLARE ms_crs_ftind CURSOR STATIC LOCAL FOR
SELECT t.name, SCHEMA_NAME(t.schema_id), ft.change_tracking_state
FROM sys.fulltext_indexes AS ft
JOIN sys.tables AS t
ON (ft.object_id = t.object_id);
OPEN ms_crs_ftind;
FETCH ms_crs_ftind INTO @table_name, @schema_name, @change_tracking_state;
WHILE @@FETCH_STATUS >= 0
BEGIN
-- Start full-text index population for each full-text index.
SELECT @exec_str = 'ALTER FULLTEXT INDEX ON '
+ QUOTENAME(@schema_name,'[')+'.'+QUOTENAME(@table_name,'[')
+ ' start full POPULATION ';
EXEC (@exec_str);
FETCH ms_crs_ftind INTO @table_name,@schema_name, @change_tracking_state;
END
DEALLOCATE ms_crs_ftind;

--For stop, just replace 'start full' with 'STOP'