SQL SERVER Interview Questions | SQL SERVER – Interview Questions and Answers – Frequently Asked Questions (Page-III)

SQL SERVER Interview Questions | SQL SERVER – Interview Questions and Answers – Frequently Asked Questions 

(Page-III)

41. What is a view?

A view is simply a virtual table that is made up of elements of multiple physical or “real” tables. Views are most commonly used to join multiple tables together, or control access to any tables existing in background server processes.

42. What is a Query Execution Plan?

SQL Server has several built-in tools that optimize how queries are executed within their databases. A query execution plan is exactly what it sounds like – a snapshot of how the optimizing tools will execute and deploy specific queries within the database. This service helps you troubleshoot problems with jobs that don’t necessarily execute perfectly.

43. What is the default port number for SQL Server?

While this is kind of a softball question – if you know anything about SQL Server you should at least know the basic configuration options – it’s an important one to nail in the interview. Basically, when SQL Server is enabled the server instant listens to the TCP port 1433.

44. What is RDBMS?
Relational Data Base Management Systems (RDBMS) are database management systems that maintain data records and indices in tables. Relationships may be created and maintained across and among the data and tables. In a relational database, relationships between data items are expressed by means of tables. Interdependencies among these tables are expressed by data values rather than by pointers. This allows a high degree of data independence. An RDBMS has the capability to recombine the data items from different files, providing powerful tools for data usage.

45. What are the Properties of the Relational Tables?
Relational tables have the following six properties:
Values are atomic.
Column values are of the same kind.
Each row is unique.
The sequence of columns is insignificant.
The sequence of rows is insignificant.
Each column must have a unique name.

46.What is Normalization?
Database normalization is a data design and organization process applied to data structures based on rules that help building relational databases. In relational database design, the process of organizing data to minimize redundancy is called normalization. Normalization usually involves dividing a database into two or more tables and defining relationships between the tables. The objective is to isolate data so that additions, deletions, and modifications of a field can be made in just one table and then propagated through the rest of the database via the defined relationships.

47. What is De-normalization?
De-normalization is the process of attempting to optimize the performance of a database by adding redundant data. It is sometimes necessary because current DBMSs implement the relational model poorly. A true relational DBMS would allow for a fully normalized database at the logical level, while providing physical storage of data that is tuned for high performance. De-normalization is a technique to move from higher to lower normal forms of database modeling in order to speed up database access.

48.How is ACID property related to Database?
ACID (an acronym for Atomicity Consistency Isolation Durability) is a concept that Database Professionals generally look for while evaluating databases and application architectures. For a reliable database, all this four attributes should be achieved.
Atomicity is an all-or-none proposition.
Consistency guarantees that a transaction never leaves your database in a half-finished state.
Isolation keeps transactions separated from each other until they are finished.
Durability guarantees that the database will keep track of pending changes in such a way that the server can recover from an abnormal termination.

49.What are the Different Normalization Forms?
1NF: Eliminate Repeating Groups
Make a separate table for each set of related attributes, and give each table a primary key. Each field contains at most one value from its attribute domain.
2NF: Eliminate Redundant Data
If an attribute depends on only part of a multi-valued key, then remove it to a separate table.
3NF: Eliminate Columns Not Dependent On Key
If attributes do not contribute to a description of the key, then remove them to a separate table. All attributes must be directly dependent on the primary key.
BCNF: Boyce-Codd Normal Form
If there are non-trivial dependencies between candidate key attributes, then separate them out into distinct tables.
4NF: Isolate Independent Multiple Relationships
No table may contain two or more 1:n or n:m relationships that are not directly related.
5NF: Isolate Semantically Related Multiple Relationships
There may be practical constrains on information that justify separating logically related many-to-many relationships.
ONF: Optimal Normal Form
A model limited to only simple (elemental) facts, as expressed in Object Role Model notation.
DKNF: Domain-Key Normal Form
A model free from all modification anomalies is said to be in DKNF.
Remember, these normalization guidelines are cumulative. For a database to be in 3NF, it must first fulfill all the criteria of a 2NF and 1NF database.

50. What is a Stored Procedure?
A stored procedure is a named group of SQL statements that have been previously created and stored in the server database. Stored procedures accept input parameters so that a single procedure can be used over the network by several clients using different input data. And when the procedure is modified, all clients automatically get the new version. Stored procedures reduce network traffic and improve performance. Stored procedures can be used to help ensure the integrity of the database.
e.g. sp_helpdb, sp_renamedb, sp_depends etc.

SQL SERVER Interview Questions | SQL SERVER – Interview Questions and Answers – Frequently Asked Questions (Page-II)

SQL SERVER Interview Questions | SQL SERVER – Interview Questions and Answers – Frequently Asked Questions (Page-II)

21. What is PRIMARY KEY?

A PRIMARY KEY constraint is a unique identifier for a row within a database table. Every table should have a primary key constraint to uniquely identify each row and only one primary key constraint can be created for each table. The primary key constraints are used to enforce entity integrity.

22. What is UNIQUE KEY constraint?

A UNIQUE constraint enforces the uniqueness of the values in a set of columns, so no duplicate values are entered. The unique key constraints are used to enforce entity integrity as the primary key constraints.

23. What is FOREIGN KEY?

A FOREIGN KEY constraint prevents any actions that would destroy links between tables with the corresponding data values. A foreign key in one table points to a primary key in another table. Foreign keys prevent actions that would leave rows with foreign key values when there are no primary keys with that value. The foreign key constraints are used to enforce referential integrity.

24. What is CHECK Constraint?

A CHECK constraint is used to limit the values that can be placed in a column. The check constraints are used to enforce domain integrity.

25. What is NOT NULL Constraint?

A NOT NULL constraint enforces that the column will not accept null values. The not null constraints are used to enforce domain integrity, as the check constraints.

26. How to get @@ERROR and @@ROWCOUNT at the same time?

If @@Rowcount is checked after Error checking statement then it will have 0 as the value of @@Recordcount as it would have been reset. And if @@Recordcount is checked before the error-checking statement then @@Error would get reset. To get @@error and @@rowcount at the same time do both in same statement and store them in local variable.

SELECT @RC = @@ROWCOUNT, @ER = @@ERROR

27. What is a Scheduled Jobs or What is a Scheduled Tasks?

Scheduled tasks let user automate processes that run on regular or predictable cycles. User can schedule administrative tasks, such as cube processing, to run during times of slow business activity. User can also determine the order in which tasks run by creating job steps within a SQL Server Agent job. E.g. back up database, Update Stats of Tables. Job steps give user control over flow of execution. If one job fails, user can configure SQL Server Agent to continue to run the remaining tasks or to stop execution.

28. What are the advantages of using Stored Procedures?

1.    Stored procedure can reduced network traffic and latency, boosting application performance.

2.    Stored procedure execution plans can be reused, staying cached in SQL Server's memory, reducing server overhead.

3.    Stored procedures help promote code reuse.

4.    Stored procedures can encapsulate logic. You can change stored procedure code without affecting clients.

5.    Stored procedures provide better security to your data.

29. What is a table called, if it has neither Cluster nor Non-cluster Index? What is it used for?

Unindexed table or Heap. Microsoft Press Books and Book on Line (BOL) refers it as Heap. A heap is a table that does not have a clustered index and, therefore, the pages are not linked by pointers. The IAM pages are the only structures that link the pages in a table together. Unindexed tables are good for fast storing of data. Many times it is better to drop all indexes from table and then do bulk of inserts and to restore those indexes after that.

30. Can SQL Servers linked to other servers like Oracle?

SQL Server can be linked to any server provided it has OLE-DB provider from Microsoft to allow a link. E.g. Oracle has an OLE-DB provider for oracle that Microsoft provides to add it as linked server to SQL Server group.

31. What is BCP? When does it used?

BulkCopy is a tool used to copy huge amount of data from tables and views. BCP does not copy the structures same as source to destination. BULK INSERT command helps to import a data file into a database table or view in a user-specified format.

32. How to 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.

33. What is an execution plan? When would you use it? How would you view the execution plan?

An execution plan is basically a road map that graphically or textually shows the data retrieval methods chosen by the SQL Server query optimizer for a stored procedure or ad- hoc query and is a very useful tool for a developer to understand the performance characteristics of a query or stored procedure since the plan is the one that SQL Server will place in its cache and use to execute the stored procedure or query. From within Query Analyzer is an option called "Show Execution Plan" (located on the Query drop-down menu). If this option is turned on it will display query execution plan in separate window when query is ran again.

34. What are DMVs?

Dynamic Management Views (DMVs), are functions that give you information on the state of the server. DMVs, for the most part, are used to monitor the health of a server. They really just give you a snapshot of what’s going on inside the server. They let you monitor the health of a server instance, troubleshoot major problems and tune the server to increase performance.

35. Define a temp table

In a nutshell, a temp table is a temporary storage structure. What does that mean? Basically, you can use a temp table to store data temporarily so you can manipulate and change it before it reaches its destination format.

36. What’s the difference between a local  temp table and a global temp table?

Local tables are accessible to a current user connected to the server. These tables disappear once the user has disconnected from the server. Global temp tables, on the other hand, are available to all users regardless of the connection. These tables stay active until all the global connections are closed.

37. How do you use transactions?

In general, there are three types of transactions that you can use in the SQL Server environment: BEGIN TRANSACTION, ROLL BACK TRANSACTION and COMMIT TRANSACTION. The gist behind deploying transactions is that they allow you to group multiple SQL commands into a single unit. From there, each transaction begins with a certain task, and ends when all the tasks within the transaction are complete. BEGIN TRANSACTION gets the ball rolling. ROLLBACK TRANSACTION functions a lot like an “undo” command, and COMMIT TRANSACTION completes all of the tasks within that transaction.

38. What’s the difference between a clustered and a non-clustered index?

A clustered index directly affects the way tabled data is stored on a specific disk. This means that when a clustered index is used, data is stored in sequential rows based on the index column value. This is why a table can only contain a single clustered index. Non-clustered indexes directly affect the way physical data is stored and managed within SQL Server.

39. What are DBCC commands?

In very basic terms the Database Consistency Checker (DBCC) is used to aid in server maintenance. DBCC commands, many of which are completely undocumented, provide a set of commands that let you perform routing maintenance, status and validation checks. The most common DBCC commands are: DBCC CHECKALLOC (Lets you check disk allocation); DBCC OPENTRAN (Lets you check any open transactions); and DBCC HELP (shows a list of available DBCC commands to aid your server maintenance processes).

40. Describe the difference between truncate and delete.

The difference between these two processes is fairly simple. Truncate means to simply empty out a table. On the other hand, the delete command lets you delete entire rows from within a table, but not all of the data within that table.

<< Page - I

SQL SERVER Interview Questions | SQL SERVER – Interview Questions and Answers – Frequently Asked Questions (Page-I)

SQL Server Interview Questions | SQL SERVER – Interview Questions and Answers – Frequently Asked Questions (Page-I)

1. Which TCP/IP port does SQL Server run on? How can it be changed?

SQL Server runs on port 1433. It can be changed from the Network Utility TCP/IP properties.

2. What are the difference between clustered and a non-clustered index?

1.    A clustered index is a special type of index that reorders the way records in the table are physically stored. Therefore table can have only one clustered index. The leaf nodes of a clustered index contain the data pages.

2.    A non-clustered index is a special type of index in which the logical order of the index does not match the physical stored order of the rows on disk. The leaf node of a non-clustered index does not consist of the data pages. Instead, the leaf nodes contain index rows.

3. What are the different index configurations a table can have?

A table can have one of the following index configurations:

1.    No indexes

2.    A clustered index

3.    A clustered index and many non-clustered indexes

4.    A non-clustered index

5.    Many non-clustered indexes

4. What are different types of Collation Sensitivity?

1.    Case sensitivity - A and a, B and b, etc.

2.    Accent sensitivity

3.    Kana Sensitivity - When Japanese kana characters Hiragana and Katakana are treated differently, it is called Kana sensitive.

4.    Width sensitivity - A single-byte character (half-width) and the same character represented as a double-byte character (full-width) are treated differently than it is width sensitive.

5. What is OLTP (Online Transaction Processing)?

In OLTP - online transaction processing systems relational database design use the discipline of data modeling and generally follow the Codd rules of data normalization in order to ensure absolute data integrity. Using these rules complex information is broken down into its most simple structures (a table) where all of the individual atomic level elements relate to each other and satisfy the normalization rules.

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

Both primary key and unique key enforces 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 non-clustered index by default. Another major difference is that, primary key doesn't allow NULLs, but unique key allows one NULL only.

7. What is difference between DELETE and TRUNCATE commands?

Delete command removes the rows from a table based on the condition that we provide with a WHERE clause. Truncate will actually remove all the rows from a table and there will be no data in the table after we run the truncate command.

1.    TRUNCATE:

1.    TRUNCATE is faster and uses fewer system and transaction log resources than DELETE.

2.    TRUNCATE removes the data by de-allocating the data pages used to store the table's data, and only the page de-allocations are recorded in the transaction log.

3.    TRUNCATE removes all rows from a table, but the table structure, its columns, constraints, indexes and so on, remains. The counter used by an identity for new rows is reset to the seed for the column.

4.    You cannot use TRUNCATE TABLE on a table referenced by a FOREIGN KEY constraint. Because TRUNCATE TABLE is not logged, it cannot activate a trigger.

5.    TRUNCATE cannot be rolled back.

6.    TRUNCATE is DDL Command.

7.    TRUNCATE Resets identity of the table

2.    DELETE:

1.    DELETE removes rows one at a time and records an entry in the transaction log for each deleted row.

2.    If you want to retain the identity counter, use DELETE instead. If you want to remove table definition and its data, use the DROP TABLE statement.

3.    DELETE Can be used with or without a WHERE clause

4.    DELETE Activates Triggers.

5.    DELETE can be rolled back.

6.    DELETE is DML Command.

7.    DELETE does not reset identity of the table.

Note: DELETE and TRUNCATE both can be rolled back when surrounded by TRANSACTION if the current session is not closed. If TRUNCATE is written in Query Editor surrounded by TRANSACTION and if session is closed, it cannot be rolled back but DELETE can be rolled back.

8. When is the use of UPDATE_STATISTICS command?

This command is basically used when a large processing of data has occurred. If a large amount of deletions any modification or Bulk Copy into the tables has occurred, it has to update the indexes to take these changes into account. UPDATE_STATISTICS updates the indexes on these tables accordingly.

9. What is the difference between a HAVING CLAUSE and a WHERE CLAUSE?

They specify a search condition for a group or an aggregate. But the difference is that HAVING can be used only with the SELECT statement. HAVING is typically used in a GROUP BY clause. When GROUP BY is not used, HAVING behaves like a WHERE clause. Having Clause is basically used only with the GROUP BY function in a query whereas WHERE Clause is applied to each row before they are part of the GROUP BY function in a query.

10. What are the properties and different Types of Sub-Queries?

1.    Properties of Sub-Query

1.    A sub-query must be enclosed in the parenthesis.

2.    A sub-query must be put in the right hand of the comparison operator, and

3.    A sub-query cannot contain an ORDER-BY clause.

4.    A query can contain more than one sub-query.

2.    Types of Sub-Query

1.    Single-row sub-query, where the sub-query returns only one row.

2.    Multiple-row sub-query, where the sub-query returns multiple rows,. and

3.    Multiple column sub-query, where the sub-query returns multiple columns

11. What is SQL Profiler?

SQL Profiler is a graphical tool that allows system administrators to monitor events in an instance of Microsoft SQL Server. You can capture and save data about each event to a file or SQL Server table to analyze later. For example, you can monitor a production environment to see which stored procedures are hampering performances by executing too slowly.

Use SQL Profiler to monitor only the events in which you are interested. If traces are becoming too large, you can filter them based on the information you want, so that only a subset of the event data is collected. Monitoring too many events adds overhead to the server and the monitoring process and can cause the trace file or trace table to grow very large, especially when the monitoring process takes place over a long period of time.

12. What are the authentication modes in SQL Server? How can it be changed?

Windows mode and Mixed Mode - SQL and Windows. To change authentication mode in SQL Server click Start, Programs, Microsoft SQL Server and click SQL Enterprise Manager to run SQL Enterprise Manager from the Microsoft SQL Server program group. Select the server then from the Tools menu select SQL Server Configuration Properties, and choose the Security page.

13. Which command using Query Analyzer will give you the version of SQL server and operating system?

SELECT SERVERPROPERTY ('productversion'), SERVERPROPERTY ('productlevel'), SERVERPROPERTY ('edition').

14. What is SQL Server Agent?

SQL Server agent plays an important role in the day-to-day tasks of a database administrator (DBA). It is often overlooked as one of the main tools for SQL Server management. Its purpose is to ease the implementation of tasks for the DBA, with its full- function scheduling engine, which allows you to schedule your own jobs and scripts.

15. Can a stored procedure call itself or recursive stored procedure? How much level SP nesting is possible?

Yes. Because Transact-SQL supports recursion, you can write stored procedures that call themselves. Recursion can be defined as a method of problem solving wherein the solution is arrived at by repetitively applying it to subsets of the problem. A common application of recursive logic is to perform numeric computations that lend themselves to repetitive evaluation by the same processing steps. Stored procedures are nested when one stored procedure calls another or executes managed code by referencing a CLR routine, type, or aggregate. You can nest stored procedures and managed code references up to 32 levels.

16. What is Log Shipping?

Log shipping is the process of automating the backup of database and transaction log files on a production SQL server, and then restoring them onto a standby server. Enterprise Editions only supports log shipping. In log shipping the transactional log file from one server is automatically updated into the backup database on the other server. If one server fails, the other server will have the same db and can be used this as the Disaster Recovery plan. The key feature of log shipping is that it will automatically backup transaction logs throughout the day and automatically restore them on the standby server at defined interval.

17. Name 3 ways to get an accurate count of the number of records in a table?

SELECT * FROM table1
SELECT COUNT(*) FROM table1
SELECT rows FROM sysindexes WHERE id = OBJECT_ID(table1) AND indid < 2

18. What does it mean to have QUOTED_IDENTIFIER ON? What are the implications of having it OFF?

When SET QUOTED_IDENTIFIER is ON, identifiers can be delimited by double quotation marks, and literals must be delimited by single quotation marks. When SET QUOTED_IDENTIFIER is OFF, identifiers cannot be quoted and must follow all Transact-SQL rules for identifiers.

19. What is the difference between a Local and a Global temporary table?

1.    A local temporary table exists only for the duration of a connection or, if defined inside a compound statement, for the duration of the compound statement.

2.    A global temporary table remains in the database permanently, but the rows exist only within a given connection. When connection is closed, the data in the global temporary table disappears. However, the table definition remains with the database for access when database is opened next time.

20. What is the STUFF function and how does it differ from the REPLACE function?

STUFF function is used to overwrite existing characters. Using this syntax, STUFF (string_expression, start, length, replacement_characters), string_expression is the string that will have characters substituted, start is the starting position, length is the number of characters in the string that are substituted, and replacement_characters are the new characters interjected into the string. REPLACE function to replace existing characters of all occurrences. Using the syntax REPLACE (string_expression, search_string, replacement_string), where every incidence of search_string found in the string_expression will be replaced with replacement_string.

Page - II >>

Embedding a PDF or other Documents into a Blogger Blog | How to add a PDF file into a blog

Embedding a PDF or other Documents into a Blogger Blog

From time to time we may be sent or create a document in Word or PDF or even Powerpoint format that we would like to display on our blog. (It's a common question that comes up a lot in the Blogger Help Forums).

This simple and quick guide will take you through the process.

So read on...

1) We want to upload our file to Google Docs. So go to  https://docs.google.com/

Note: Depending on if you use Google Drive the screenshots may say either Google Drive or Google Docs. They are in essence the same thing.

2) Click the Upload Icon and select files.

3) Pick the PDF or other file you want to embed and click Open

4) You'll be presented with a confirmation box. Press the Start Upload button.

5) You'll be presented with an Upload Progress box

6) When that has finished click the filename.

7) This will load the File into your Google Doc/Drive screen. Now we need to "Share" the file so that it will be visible to your readers on your blog. Click the Blue Share button at the Top Right.

8) You will then be presented with the Share Dialogue screen. Click the Change link.

9) Select "Public on the web" and press Save followed by Done.

10) Now we want to grab the Embed Code that we will use to post onto our Blog. Click the File menu then Embed option.

11) You will then be presented with the Embed code. Copy the code by selecting it all and pressing CTRL-C

12) Now goto your Blog and create a New Post and make sure you are on the HTML Tab. In the Blog Post section Paste in your embed code. It should look like this.

NOTE: You can alter the width="640" height="480" parts of the embed code to fit the size of your blog.

13) Click the Preview Button and you should see your PDF embedded in your Blog Post. If everything is ok you can go ahead and publish your post.

And that's it.

So in summary...

1) Upload the file
2) Share the File and get the Embed code
3) Post the embed code to your blog.

How To Schedule Computer To Shut Down At A Certain Time

What Operating System is installed in your machine?

If using Windows 7, follow these steps to schedule your PC(Personal Computer) to shut down at a certain time at night:

1. Go to Start > Control Panel > System and Security > Administrative Tools and click on the Task Scheduler.

2. From the Action menu in Task Scheduler, click "Create Basic Task..."

3. In the "Create Basic Task Wizard" windows that pops up, Type in a title and a description. Something basic like "PC Shutdown."

4. Click "Next."

5. On the "Task Trigger" screen, choose the frequency with which you want the Shutdown PC to run. For nightly shutdown, click on "daily" and click the Next" button.

6.On the "Daily" screen, enter the date and time you want your PC to shutdown. Click "Next."

7. On the "Action" screen, choose "Start a program" and click "Next."

8. On the "Start a Program" screen, type C:\Windows\System32\shutdown.exe in the "Program/script" text field.

9. In the Add arguments text field type /s.

10. Click "Next."

11. Confirm your settings on the Summary screen and click "Finish."

Now your Windows 7 computer will automatically shutdown at the same time every day/night.