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SQL SERVER INTERVIEW QUESTIONS 2014 BOOKLET -4 By Mr.J.Venkatesan Prabu - Managing Director of Kaashiv Infotech

            
      SQL SERVER INTERVIEW QUESTIONS 2014- SET 4 By 
"Mr.J.Venkatesan Prabu" 

KAASHIV INFOTECH

     [ The  Asia, India & Tamil Nadu Book Of  Record Holders ]


                                                       
    SQL Server Interview Questions 2014
SQL  SERVER –Booklet 4
-         Gives you the interview tips for SQL Server

 SQL SERVER INTERVIEW QUESTIONS WITH ANSWERS 

1. Explain the following.
a.) COLLATION.
Collation is a type of sort order. There are mainly three types of sort orders, namely:
i.) Dictionary case sensitive
ii.)Dictionary - case insensitive
iii.)Binary.
b.) Stored Procedure
- It is a set of T-SQL statements combined together to perform a single task formed by combining many small tasks.
- When you actually run a Stored procedure, a set of statements is run.

2. What do you mean by ACID?
- ACID (Atomicity Consistency Isolation Durability) is a quality sought after in a reliable database. Here's the relevance of each quality:
- Atomicity is an all-or-none proposition.
- Consistency - it guarantees that your database is never left by a transaction in a half-finished state.
- Isolation - it keeps transactions separated from each other until they’re finished.
- Durability - it ensures that the database keeps a track of pending changes in a way that the server can recover from an abnormal termination.
3. Explain the following:
a.) Dirty pages.
These are the buffer pages that contain modifications which have not been written to disk.
b.) ETL - Extraction, Transformation, and Loading.
- It is the process of copying and cleaning data from heterogeneous sources.
- It is an important part of development projects for data warehousing and business intelligence.

4. Differentiate between a Local and a Global temporary table?
- 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.
- Global temporary tables (created with a double “##”) are visible to all sessions.
- Global temporary tables are dropped when the session that created it ends, and all other sessions have stopped referencing it.

5. Explain different types of Locks in SQL Server.
There are 3 kinds of locks in SQL Server
i.) Shared locks - they are used for operations which do not allow any change or update of data. For e.g. SELECT.
ii.) Update locks - they are used when SQL Server wants to modify a page. The update page lock is then promoted to an exclusive page lock before actually making the changes.
iii.) Exclusive locks - they are used for the data modification operations. For e.g. UPDATE, INSERT, or DELETE

6.What is trigger? 
Triggers allows us to execute a batch of SQL code when either an insert, update or delete command is executed against a specific table.

Triggers are special types of stored procedures that are defined to execute automatically in place of or after data modifications. They can be executed automatically on the insert, delete and update operation.

7.How many types of triggers are there?
There are four types of triggers.

1. Insert
2. Delete
3. Update
4. Instead of

8.What is constraints?
SQL Server users constraints to  enforce limitations on the data that can be          entered into a particular column in table. There are following types of constraints.

      Unique, Default, Check, Primary Key, Foreign Key, Not Null.


9. How to join two tables in Sql Server?

you can write following sql statement

select category.*, categoryparent.categoryparent from category, categoryparent where category.categoryparentid = categoryparent.autoid

I am assuming here that category.categoryparentid (foreign key) is the value of categoryparent.autoid (primary key).

10.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".

11.Difference Between Implict Transaction And Explict Transaction

Implicit Transaction is the auto commit. There is no beginning or ending of the transaction. 

Explicit Transaction has the beginning, ending and rollback of transactions with the command 
Begin Transaction 
Commit Transaction and 
Rollback Transation 
In the explicit transaction, if an error occurs in between we can rollback to the beginning of the transaction which cannot be done in implicit transaction.


12.what is the diff between a HAVING CLAUSE and a WHERE CLAUSE?
You can use Having Clause with the GROUP BY function in query and WHERE Clause is applied to each row before they are part of the GROUP BY function in a query.

13.How to change Database name in SQL Server?
Use following code
Supported in SQL Server 2000 and 2005
exec sp_renamedb "test", "test1"
Supported in SQL Server 2005 and later version
ALTER Database "test1" Modify Name="test"

14.Write SQL Query to display current date.

 SQL has built in function called GetDate () which returns current timestamp.

15.When do you use UPDATE_STATISTICS command?

 This command is used when a large processing of data has occurred. If any large amount of deletions, any modifications, 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.

16.How to create recursive query in SQL Server?

 Recursive query can be create in SQL using stored procedure but you can also use CTE (Common table expression). It might be also worth asking about performance as CTE is not always very fast.

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My T-SQL Gallery @code.msdn.microsoft


Created my own T-SQL Gallery in Microsoft site. Do visit the same and share your feedback,

http://code.msdn.microsoft.com/VenkatSQLSample/Thread/List.aspx

Thanks and Regards,
Venkatesan Prabu .J

SQL Server Interview questions - Part 1

What is the significance of NULL value and why should we avoid permitting null values?
Null means no entry has been made. It implies that the value is either unknown or undefined.We should avoid permitting null values because Column with NULL values can't have PRIMARY KEY constraints. Certain calculations can be inaccurate if NULL columns are involved.

What is SQL whats its uses and its component ?
The Structured Query Language (SQL) is foundation for all relational database systems. Most of the large-scale databases use the SQL to define all user and administrator interactions. It enable us to retrieve the data from based on our exact requirement. We will be given a flexibility to store the data in our own format.


The DML component of SQL comprises four basic statements:
* SELECT to get rows from tables
* UPDATE to update the rows of tables
* DELETE to remove rows from tables
* INSERT to add new rows to tables


What is DTS in SQL Server ?
Data Transformation Services is used to transfer the data from one source to our required destination. Considering am having some data in sql server and I need to transfer the data to Excel destination. Its highly possible with dialogue based tool called Data Transformation services. More customization can be achieved using SSIS. A specialized tool used to do such migration works.


What is the difference between SQL and Pl/Sql ?

Straight forward. SQL is a single statement to finish up our work.Considering, I need some data from a particular table. “Select * from table” will fetch the necessary information. Where as I need to do some row by row processing. In that case, we need to go for Procedural Logic / SQL.

What is the significance of NULL value and why should we avoid permitting null values?
Null means no entry has been made. It implies that the value is either unknown or undefined.We should avoid permitting null values because Column with NULL values can't have PRIMARY KEY constraints. Certain calculations can be inaccurate if NULL columns are involved.

Difference between primary key and Unique key?
Both constraints will share a common property called uniqueness. The data in the column should be unique. The basic difference is,
· Primary key won’t allow null value. Whereas, unique key will accept null value but only one null value.
· On creating primary key, it will automatically format the data inturn creates clustered index on the table. Whereas, this characteristics is not associated with unique key.
· Only one primary key can be created for the table. Any number of Unique key can be created for the table.

Select Statement in SQL Server

Select Statement in SQL Server

String Functions in sql server

String Functions in sql server
Substring/Len/replace/Ltrim/Rtrim

SQL Server Interview Question - Part 2

What is normalization?

Normalization is the basic concept used in designing a database. Its nothing but, an advise given to the database to have minimal repetition of data, highly structured, highly secured, easy to retrieve. In high level definition, the Process of organizing data into tables is referred to as normalization.


What is a stored procedure:
Stored procedures are precompiled T-SQL statements combined to perform a single task of several tasks. Its basically like a Macro so when you invoke the Stored procedure, you actually run a set of statements. As, its precompiled statement, execution of Stored procedure is compatatively high when compared to an ordinary T-SQL statement.


What is the difference between UNION ALL Statement and UNION ?
The main difference between UNION ALL statement and UNION is UNION All statement is much faster than UNION,the reason behind this is that because UNION ALL statement does not look for duplicate rows, but on the other hand UNION statement does look for duplicate rows, whether or not they exist.

Example for Stored Procedure?
They are three kinds of stored procedures,1.System stored procedure – Start with sp_2. User defined stored procedure – SP created by the user.3. Extended stored procedure – SP used to invoke a process in the external systems.Example for system stored proceduresp_helpdb - Database and its propertiessp_who2 – Gives details about the current user connected to your system. sp_renamedb – Enable you to rename your database


What is a trigger?

Triggers are precompiled statements similar to Stored Procedure. It will automatically invoke for a particular operation. Triggers are basically used to implement business rules.


What is a view?
If we have several tables in a db and we want to view only specific columns from specific tables we can go for views. It would also suffice the needs of security some times allowing specfic users to see only specific columns based on the permission that we can configure on the view. Views also reduce the effort that is required for writing queries to access specific columns every time.


What is an Index?
When queries are run against a db, an index on that db basically helps in the way the data is sorted to process the query for faster and data retrievals are much faster when we have an index.


What are the types of indexes available with SQL Server?

There are basically two types of indexes that we use with the SQL ServerClustered -

1. It will format the entire table, inturn physically sort the table.

2. Only one clustered index can be created for a table.

3. Data will be located in the leaf level.

4. By default, primary key will create clustered index on the table.

Non-Clustered Index

1. It wont touch the structure of the table.

2. It forms an index table as reference to the exact data.

3. A reference to the data will be located in the leaf level.

4. For a table, we can create 249 non clustered index.

Happy Learning!!!
Regards,
Venkatesan Prabu .J

SQL Interview question

Extent Vs Page?

Pages are low level unit to store the exact data in sql server. Basically, the data will be stored in the mdf, ldf, ndf files. Inturn, pages are logical units available in sql server.The size of the page is 8KB.

Eight consecutive pages will form an extent 8 * 8KB = 64KB.

Thus I/O level operation will be happening at pages level.The pages will hold a template information at the start of each page (header of the page).

They are,

1. page number,

2. page type,

3. the amount of free space on the page,

4. the allocation unit ID of the object that owns the page.

Extents will be classifed into two types,

1. Uniform extents

2. Mixed extents

Uniform Extents:It occupied or used by a single object. Inturn, a single object will hold the entire 8 pages.Mixed

Extents:Mulitple objects will use the same extent. SQL Server will allow a max of eight objects to use a shared extent.

Property of SQL Server :Initally if an object is created, sql server will allocate the object to the mixed extent and once if the size reaches 8 pages and more... immediately, a new uniform extent will be provided for that particular object.

Herecomes, our fragmentation and reindexing concepts.

Best Joke - Enjoy it

Best Joke - Enjoy it