More Sql Server Questions

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.

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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.

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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.

sql -server questions

Output in Query Analyzer seems truncated. I can see only the first 255 characters per line. Maximum how many characters can be ?
Select Answer:
1. 1024
2. 1023
3. 8192
4. 8194
5. 256



How to read transaction logs from Query Analyzer ?
Select Answer:
1. DBCC READLOG (DatabaseName, 1)
2. DBCC LOG (DatabaseName, 1)
3. DBCC READLOG (DatabaseName, 3)
4. DBCC LOG (DatabaseName, 2)




How to reset or reseed the IDENTITY column?
Select Answer:
1. DBCC IDENTRESET
2. DBCC CHECKIDENTITY
3. DBCC CHECKIDENT
4. DBCC IDENTRESEED



Which one of the following is an alternate way to 'TimeStamp' Type
Select Answer:
1. Create Table MyTable (RowSeq Rowversion, Names Varchar(50))
2. Create Table MyTable (RowSeq Timestemp, Names Varchar(50))
3. Create Table MyTable (RowSeq RowNumber, Names Varchar(50))
4. Create Table MyTable (RowSeq RowSerial, Names Varchar(50))




Which one is used to invoke/instantiate COM objects from within stored procedures using T-SQL?
Select Answer:
1. sp_COMCreate
2. sp_OACreate
3. xp_COMCreate
4. sp_OACreate


How to get the complete error message from T-SQL while error handling?
Select Answer:
1. Master..SysErrors
2. Master..SysWarnings
3. Master..SysMessages
4. @@Error


How to run an SQL script file that is located on the disk, using T-SQL from Query Analyzer ?Select Answer:
1. EXEC Master..xp_cmdshell 'osql -S ServerName -U UserName -P Password -i SQL Script File Path'
2. EXEC Master..xp_cmdshell 'osql -S ServerName -U UserName -P Password -o SQL Script File Path'
3. EXEC Master..xp_cmdshell 'osql -S ServerName -u UserName -p Password -i SQL Script File Path'
4. EXEC Master..xp_cmdshell 'sql -S ServerName -U UserName -P Password -i SQL Script File Path'


How to programmatically(Query) find out when the SQL Server service started?
Select Answer:
1. SELECT crdate AS 'SQL Server service started approximately at:' FROM master.dbo.sysdatabases WHERE name = 'master'
2. SELECT crdate AS 'SQL Server service started approximately at:' FROM master.dbo.sysdatabases WHERE name = 'tempdb'
3. SELECT crdate AS 'SQL Server service started approximately at:' FROM master.dbo.sysdatabases WHERE name = 'model'
4. SELECT crdate AS 'SQL Server service started approximately at:' FROM master.dbo.sysdatabases WHERE name = 'msdb'

how many clustered index per table?
Select Answer:
1. 1
2. 2
3. 5
4. 10




How many Columns per SELECT statement its possible?
Select Answer:
1. 3052
2. 2048
3. 1024
4. 4,096



what is the maximum database size?
Select Answer:
1. 1,048,516 terabytes
2. 1,048,518 terabytes
3. 1,048,517 terabytes
4. 1,048,519 terabytes


What is the maximum size of row?
Select Answer:
1. 8060 bytes
2. 8060 kilo bytes
3. 8060 terra bytes
4. 8060 mega bytes


what is the maximum no of columns can a table have?
Select Answer:
1. 1012
2. 1024
3. 1000
4. 1050




What is the row size in SQL Server 2000?
Select Answer:
1. 1024 bytes.
2. 8060 bytes.
3. 6040 bytes.
4. 256 bytes.


Explain ACID in SQL?
Select Answer:
1. A: Automatic; C:Computing; I: Independent; D: Data base
2. A: Assembly; C: Copied to; I:Isolated; D:Destination
3. A: Atomic; C: Consistent; I: Isolated; D: Durable
4. A: Always; C: Copy to; I: Intermediate; D: Data base



‘What is difference between EquiJoin and Self Join
Select Answer:
1. EquiJoin means join two table based on Equality Condition
2. Self join means join table itself
3. answer1 and Answer 2 correct
4. only Answer two correct


Does unique key alllows NULL values?
Select Answer:
1. YES.It can allow as many nulls
2. NO
3. YES .It allows only one NULL value


In SQL Server Table Hint - Which one of the following is Equivalent to 'NOLOCK' ?
Select Answer:
1. HOLDLOCK
2. READCOMMITTED
3. READUNCOMMITTED
4. READCOMMITTEDLOCK


What is the maximum character length for the nchar or nvarchar datatype?
Select Answer:
1. 255
2. 1000
3. 2000
4. 4000
5. 8000

During delete trigger statement processing, where all deleted rows stored?
Select Answer:
1. Inserted table
2. Deleted table
3. #inserted table
4. #deleted table
5. Updated table


Mr.Setaceo trying to specify the order of Trigger(TR_ONE) to be executed @ FIRST. When doing so, Which one the following Err will occur ?Note: Trigger(TR_ONE) not yet been created.
Select Answer:
1. Could not find a trigger named 'TR_ONE'
2. Could not find a table or object named 'TR_ONE'. Check sysobjects.
3. Could not find a trigger or object named 'TR_ONE'. Check sysobjects.
4. Could not find a table named 'TR_ONE'

How many stored procedures can be called from a single stored procedure
Select Answer:
1. 23
2. 32
3. 34
4. 24
5. 36

Which ConnectionString is used to access the remote SQL Server database?
Select Answer:
1. Server=myServerAddress;Database=myDataBase;Integrated Security=True;Asynchronous Processing=True;
2. Data Source=IPAddress,1433;Network Library=DBMSSOCN;Initial Catalog=myDataBase;User ID=myUsername;Password=myPassword;
3. Server=myServerAddress;Database=myDataBase;Trusted_Connection=True;MultipleActiveResultSets=true;
4. Server=myServerAddress;Database=myDataBase;Trusted_Connection=True;

Sql Server questions:

1. Which statements should you use to return only the ten rows from the Products table?

ANS: select TOP 10 page_id from page

2. Select all types for which there are more than one book titles?

Titles Table

Title_id	Tid (varchar)
Title	Varchar (80)
Type	Char (12)

ANS:

SELECT type,count(title) FROM Titles

GROUP BY title

HAVING count(title) > 1

3. Select all Authors who live in the same city and state as publisher.

Authors Table

Au_id	Id (varchar)
Au_lname	Varchar (40)
Au_fname	Varchar (20)
City	Varchar (20)
State	Char (2)

Publishers Table

pub_id	Id (varchar)
pub_name	Varchar (40)
City	Varchar (20)
State	Char (2)

ANS:

 SELECT Au_lname from Authors a

 Inner join  Publishers p on a.City = p.city and a.State = p.State

4. Sub Query

Question: Get the second largest price product from products table.

Products

ProductID	Int
ProductName	Varchar (40)
UnitPrice	Money (8)

Answer:

select max(page_id) from page

where page_id not in (select max(page_id) from page )

5. Select all products having UnitPrice between 100 and 500?

Products

ProductID	Int
ProductName	Varchar (40)
UnitPrice	Money (8)

ANS:

select page_id from page

where page_id between 3 and 12

6.Get list of products by Ascending order of product name and descending order of unit price.

Products

ProductID	Int
ProductName	Varchar (40)
UnitPrice	Money (8)

ANS:

select page_id,page_name from page

order by page_id asc, page_name DESC

7. What result you will get by following query?

Products

ProductID	Int
ProductName	Varchar (40)
UnitPrice	Money (8)

SELECT * FROM Products WHERE ProductName Like ‘[a-z]%’

ANS:

Only start with any a-z alphabet character.

8. What will be result of following statement?

SELECT ProductName as Test FROM Products GROUP BY Test

ANS:

Invalid column name 'Test'.

9. Get unique type names from Titles table.

Titles Table

Title_id	Tid (varchar)
Title	Varchar (80)
Type	Char (12)

Records:

Title_id Title Type

BU1032 The Busy Executive's business

BU1111 Cooking with Computers business

MC2222 Silicon Valley Gastronomic mod_cook

MC3021 The Gourmet Microwave mod_cook

MC3026 The Psychology of Computer UNDECIDED

PS2091 Is Anger the Enemy? psychology

PS2106 Life Without Fear psychology

ANS:

SELECT distinct Type from Titles

10. Get all Authors for which titles are present?

authors

au_id	id (varchar)
au_lname	Varchar(40)
au_fname	Varchar(20)

Titleauthor

au_id	id (varchar)
Title_id	tid (varchar)
au_ord	tinyint

ANS:

SELECT a.au_lname, a.au_fname

FROM authors a

INNER JOIN Titleauthor ta ON a.au_id = ta. .au_id

1. Write a statement that will return ProductID and Name from Products table for whose UnitPrice exceeds $40, also sort the result by Name in ascending order.

ANS: Select ProductID, Name From Products Where UnitPrice>40 Order by Name asc

2. Write a statement that will return the Names of all employees whose salary are equal to maximum salary paid by company.

Employee

ID	Int
FirstName	Varchar (50)
LastName	Varchar (50)
Salary	Money

ANS: Select * From Employee where salary in (SELECT MAX(Salary) FROM Employee)

3. Retrieve Authors name and when applicable the names of any Employee that are located in the same city as Authors.

Authors

ID	Int
AuName	Varchar(50)
City	Varchar(50)

Employee

ID	Int
EmName	Varchar (50)
City	Varchar (50)

ANS: Select AuName,EmName From Author Left Outer Join Employee on Author.City = Employee.City

4. Get all records from Titles table for which Title_ID starts with ‘M’ and Type starts with ‘U’.

Titles Table

Title_id	Tid (varchar)
Title	Varchar (80)
Type	Char (12)

Records:

Title_id Title Type

BU1032 The Busy Executive's business

BU1111 Cooking with Computers business

MC2222 Silicon Valley Gastronomic mod_cook

MC3021 The Gourmet Microwave mod_cook

MC3026 The Psychology of Computer UNDECIDED

PS2091 Is Anger the Enemy? psychology

PS2106 Life Without Fear psychology

ANS: Select * From Titles where Title_ID like ‘M%’ and Type like ‘U%’

5. What will be result of following statement?

Products

ProductID	Int
ProductName	Varchar (40)
ExpiryDate	DateTime
UnitsInStock	Int

Select * from Products where (ProductID = ProductID+1)

ANS: No records.

6. Get all products from Products table for which will expire within one week from now?

Products

ProductID	Int
ProductName	Varchar (40)
ExpiryDate	DateTime
UnitsInStock	Int

ANS: Select * from products where ExpiryDate<=DATEADD(dd,7,GetDate()) AND ExpiryDate>=GetDate()

7. What will be result of following statement?

SELECT ProductName FROM Products group by ProductName,UnitsInStock having UnitsInStock>10

ANS: Unique products for which UnitsInStocks are greater than 10.

8. Get all Authors for which titles are present?

authors

au_id	id (varchar)
au_lname	Varchar(40)
au_fname	Varchar(20)

Titleauthor

au_id	id (varchar)
Title_id	tid (varchar)
au_ord	Tinyint

ANS:

SELECT * FROM authors WHERE au_id IN (SELECT au_ID FROM titleauthor)

9. Get the second minimum price product from products table.

Products

ProductID	Int
ProductName	Varchar (40)
UnitPrice	Money (8)

ANS:

SELECT MIN (a.UnitPrice) FROM Products a WHERE a.UnitPrice NOT IN (SELECT MIN (b.UnitPrice) FROM Products b)

10. Update the UnitPrice of the products named “Test Product” with the average price of products in products table.

Products

ProductID	Int
ProductName	Varchar (40)
UnitPrice	Money (8)

ANS: Update Products

set UnitPrice = (SELECT AVG (UnitPrice) From Products) Where ProductName=’Test Product’