Microsoft SQL Server
1. 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.
2. What are
the properties of the Relational tables?
Relational tables have 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.
3. 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.
4. 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.
5. What are
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, remove it to a
separate table.
- 3NF: Eliminate Columns Not Dependent On Key If
attributes do not contribute to a description of the key, 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,
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.
6. What is
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.
e.g. sp_helpdb, sp_renamedb, sp_depends etc.
7. What is
Trigger?
A trigger is a SQL procedure that initiates an
action when an event (INSERT, DELETE or UPDATE) occurs. Triggers are stored in
and managed by the DBMS. Triggers are used to maintain the referential
integrity of data by changing the data in a systematic fashion. A trigger
cannot be called or executed; DBMS automatically fires the trigger as a result
of a data modification to the associated table. Triggers can be viewed as
similar to stored procedures in that both consist of procedural logic that is
stored at the database level. Stored procedures, however, are not event-drive
and are not attached to a specific table as triggers are. Stored procedures are
explicitly executed by invoking a CALL to the procedure while triggers are
implicitly executed. In addition, triggers can also execute stored procedures.
8. What is
Nested Trigger?
A trigger can also contain INSERT, UPDATE and
DELETE logic within itself, so when the trigger is fired because of data
modification it can also cause another data modification, thereby firing
another trigger. A trigger that contains data modification logic within itself
is called a nested trigger.
9. What is
View?
A simple view can be thought of as a subset of a
table. It can be used for retrieving data, as well as updating or deleting
rows. Rows updated or deleted in the view are updated or deleted in the table
the view was created with. It should also be noted that as data in the original
table changes, so does data in the view, as views are the way to look at part
of the original table. The results of using a view are not permanently stored
in the database. The data accessed through a view is actually constructed using
standard T-SQL select command and can come from one to many different base tables
or even other views.
10. What is
Index?
An index is a physical structure containing
pointers to the data. Indices are created in an existing table to locate rows
more quickly and efficiently. It is possible to create an index on one or more
columns of a table, and each index is given a name. The users cannot see the
indexes; they are just used to speed up queries. Effective indexes are one of
the best ways to improve performance in a database application. A table scan
happens when there is no index available to help a query. In a table scan SQL
Server examines every row in the table to satisfy the query results. Table
scans are sometimes unavoidable, but on large tables, scans have a terrific
impact on performance.
11. What is
a Linked Server?
Linked Servers is a concept in SQL Server by which
we can add other SQL Server to a Group and query both the SQL Server dbs using
T-SQL Statements. With a linked server, you can create very clean, easy to
follow, SQL statements that allow remote data to be retrieved, joined and
combined with local data. Stored Procedure sp_addlinkedserver,
sp_addlinkedsrvlogin will be used add new Linked Server.
12. What is
Cursor?
Cursor is a database object used by applications to
manipulate data in a set on a row-by- row basis, instead of the typical SQL
commands that operate on all the rows in the set at one time.
In order to work with a cursor we need to perform some steps in the following order:
In order to work with a cursor we need to perform some steps in the following order:
- Declare cursor
- Open cursor
- Fetch row from the cursor
- Process fetched row
- Close cursor
- Deallocate cursor
13. What is
Collation?
Collation refers to a set of rules that determine
how data is sorted and compared. Character data is sorted using rules that
define the correct character sequence, with options for specifying case
sensitivity, accent marks, kana character types and character width.
14. What is
Difference between Function and Stored Procedure?
UDF can be used in the SQL statements anywhere in
the WHERE/HAVING/SELECT section where as Stored procedures cannot be. UDFs that
return tables can be treated as another rowset. This can be used in JOINs with
other tables. Inline UDF's can be thought of as views that take parameters and
can be used in JOINs and other Rowset operations.
15. What is
sub-query? Explain properties of sub-query?
Sub-queries are often referred to as sub-selects,
as they allow a SELECT statement to be executed arbitrarily within the body of
another SQL statement. A sub-query is executed by enclosing it in a set of
parentheses. Sub-queries are generally used to return a single row as an atomic
value, though they may be used to compare values against multiple rows with the
IN keyword.
A subquery is a SELECT statement that is nested
within another T-SQL statement. A subquery SELECT statement if executed
independently of the T-SQL statement, in which it is nested, will return a
resultset. Meaning a subquery SELECT statement can standalone and is not
depended on the statement in which it is nested. A subquery SELECT statement
can return any number of values, and can be found in, the column list of a
SELECT statement, a FROM, GROUP BY, HAVING, and/or ORDER BY clauses of a T-SQL
statement. A Subquery can also be used as a parameter to a function call.
Basically a subquery can be used anywhere an expression can be used.
16. What
are different Types of Join?
- Cross Join A cross join that does not have a WHERE
clause produces the Cartesian product of the tables involved in the join.
The size of a Cartesian product result set is the number of rows in the
first table multiplied by the number of rows in the second table. The
common example is when company wants to combine each product with a
pricing table to analyze each product at each price.
- Inner Join A join that displays only the rows that have
a match in both joined tables is known as inner Join. This is the default
type of join in the Query and View Designer.
- Outer Join A join that includes rows even if they do not
have related rows in the joined table is an Outer Join. You can create
three different outer join to specify the unmatched rows to be included:
- Left Outer Join: In
Left Outer Join all rows in the first-named table i.e. "left"
table, which appears leftmost in the JOIN clause are included. Unmatched
rows in the right table do not appear.
- Right Outer Join: In
Right Outer Join all rows in the second-named table i.e.
"right" table, which appears rightmost in the JOIN clause are
included. Unmatched rows in the left table are not included.
- Full Outer Join: In
Full Outer Join all rows in all joined tables are included, whether they
are matched or not.
- Self Join This is a particular case when one table
joins to itself, with one or two aliases to avoid confusion. A self join
can be of any type, as long as the joined tables are the same. A self join
is rather unique in that it involves a relationship with only one table.
The common example is when company has a hierarchal reporting structure
whereby one member of staff reports to another. Self Join can be Outer
Join or Inner Join.
17. What
are primary keys and foreign keys?
Primary keys are the unique identifiers for each
row. They must contain unique values and cannot be null. Due to their
importance in relational databases, Primary keys are the most fundamental of
all keys and constraints. A table can have only one Primary key. Foreign keys
are both a method of ensuring data integrity and a manifestation of the
relationship between tables.
18. What is
User Defined Functions? What kind of User-Defined Functions can be created?
User-Defined Functions allow defining its own T-SQL
functions that can accept 0 or more parameters and return a single scalar data
value or a table data type.
Different Kinds of User-Defined Functions created
are:
- Scalar User-Defined Function A
Scalar user-defined function returns one of the scalar data types. Text,
ntext, image and timestamp data types are not supported. These are the
type of user-defined functions that most developers are used to in other
programming languages. You pass in 0 to many parameters and you get a
return value.
- Inline Table-Value User-Defined Function An
Inline Table-Value user-defined function returns a table data type and is
an exceptional alternative to a view as the user-defined function can pass
parameters into a T-SQL select command and in essence provide us with a
parameterized, non-updateable view of the underlying tables.
- Multi-statement Table-Value User-Defined Function A
Multi-Statement Table-Value user-defined function returns a table and is
also an exceptional alternative to a view as the function can support
multiple T-SQL statements to build the final result where the view is
limited to a single SELECT statement. Also, the ability to pass parameters
into a TSQL select command or a group of them gives us the capability to
in essence create a parameterized, non-updateable view of the data in the
underlying tables. Within the create function command you must define the
table structure that is being returned. After creating this type of
user-defined function, It can be used in the FROM clause of a T-SQL
command unlike the behavior found when using a stored procedure which can
also return record sets.
19. What is
Identity?
Identity (or AutoNumber) is a column that
automatically generates numeric values. A start and increment value can be set,
but most DBA leave these at 1. A GUID column also generates numbers; the value
of this cannot be controlled. Identity/GUID columns do not need to be indexed.
20. What is
Data Warehousing?
- Subject-oriented, meaning that the data in the database is
organized so that all the data elements relating to the same real-world
event or object are linked together;
- Time-variant, meaning that the changes to the data in the database
are tracked and recorded so that reports can be produced showing changes
over time;
- Non-volatile, meaning that data in the database is never
over-written or deleted, once committed, the data is static, read-only,
but retained for future reporting.
- Integrated, meaning that the database contains data from most or
all of an organization's operational applications, and that this data is
made consistent
21. 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.
22. What
are the difference between clustered and a non-clustered index?
- 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.
- 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.
23. What
are the different index configurations a table can have?
A table can have one of the following index
configurations:
- No indexes
- A clustered index
- A clustered index and many nonclustered indexes
- A nonclustered index
- Many nonclustered indexes
24. What
are different types of Collation Sensitivity?
- Case sensitivity - A and a, B and b, etc.
- Accent sensitivity
- Kana Sensitivity - When Japanese kana characters Hiragana and
Katakana are treated differently, it is called Kana sensitive.
- 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.
25. 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.
26. 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 nonclustered index by
default. Another major difference is that, primary key doesn't allow NULLs, but
unique key allows one NULL only.
27. 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.
- TRUNCATE:
- TRUNCATE is faster and uses fewer system and
transaction log resources than DELETE.
- TRUNCATE removes the data by deallocating the
data pages used to store the table's data, and only the page
deallocations are recorded in the transaction log.
- 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.
- 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.
- TRUNCATE cannot be rolled back.
- TRUNCATE is DDL Command.
- TRUNCATE Resets identity of the table
- DELETE:
- DELETE removes rows one at a time and records
an entry in the transaction log for each deleted row.
- 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.
- DELETE Can be used with or without a WHERE
clause
- DELETE Activates Triggers.
- DELETE can be rolled back.
- DELETE is DML Command.
- 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 can not be rolled back but DELETE can be rolled back.
28. 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.
29. 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.
30. What
are the properties and different Types of Sub-Queries?
- Properties of Sub-Query
- A sub-query must be enclosed in the
parenthesis.
- A sub-query must be put in the right hand of
the comparison operator, and
- A sub-query cannot contain an ORDER-BY clause.
- A query can contain more than one sub-query.
- Types of Sub-Query
- Single-row sub-query, where the sub-query
returns only one row.
- Multiple-row sub-query, where the sub-query
returns multiple rows,. and
- Multiple column sub-query, where the
sub-query returns multiple columns
31. 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.
32. 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
33. Which command using Query Analyzer will give you the version
of SQL server and operating system?
SELECT SERVERPROPERTY
('productversion'), SERVERPROPERTY ('productlevel'), SERVERPROPERTY
('edition').
34. 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.
35. 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.
36. 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.
37. 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
38. 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
39. What is
the difference 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.
- 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.
40. 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.
41. 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.
42. 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.
43. 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.
44. 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.
45. 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.
46. 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
47. 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.
48. What
are the advantages of using Stored Procedures?
- Stored procedure can reduced network traffic and latency, boosting
application performance.
- Stored procedure execution plans can be reused, staying cached in
SQL Server's memory, reducing server overhead.
- Stored procedures help promote code reuse.
- Stored procedures can encapsulate logic. You can change stored
procedure code without affecting clients.
- Stored procedures provide better security to your data.
49. 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.
50. 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.
51. 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.
52. 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.
53. 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
54. What
are the basic functions for master, msdb, model, tempdb and resource databases?
- The master database holds information for all databases
located on the SQL Server instance and is theglue that holds the engine
together. Because SQL Server cannot start without a functioning
masterdatabase, you must administer this database with care.
- The msdb database stores information regarding database
backups, SQL Agent information, DTS packages, SQL Server jobs, and some
replication information such as for log shipping.
- The tempdb holds temporary objects such as global and local
temporary tables and stored procedures.
- The model is essentially a template database used in the
creation of any new user database created in the instance.
- The resoure Database is a read-only database that contains
all the system objects that are included with SQL Server. SQL Server
system objects, such as sys.objects, are physically persisted in the
Resource database, but they logically appear in the sys schema of every
database. The Resource database does not contain user data or user
metadata.
55. What is
Service Broker?
Service Broker is a message-queuing technology in
SQL Server that allows developers to integrate SQL Server fully into
distributed applications. Service Broker is feature which provides facility to
SQL Server to send an asynchronous, transactional message. it allows a database
to send a message to another database without waiting for the response, so the
application will continue to function if the remote database is temporarily
unavailable.
56. Where
SQL server user names and passwords are stored in SQL server?
They get stored in System Catalog Views
sys.server_principals and sys.sql_logins.
57. What is
Policy Management?
Policy Management in SQL SERVER 2008 allows you to
define and enforce policies for configuring and managing SQL Server across the
enterprise. Policy-Based Management is configured in SQL Server Management
Studio (SSMS). Navigate to the Object Explorer and expand the Management node
and the Policy Management node; you will see the Policies, Conditions, and Facets
nodes.
58. What is
Replication and Database Mirroring?
Database mirroring can be used with replication to
provide availability for the publication database. Database mirroring involves
two copies of a single database that typically reside on different computers.
At any given time, only one copy of the database is currently available to
clients which are known as the principal database. Updates made by clients to
the principal database are applied on the other copy of the database, known as
the mirror database. Mirroring involves applying the transaction log from every
insertion, update, or deletion made on the principal database onto the mirror
database.
59. What
are Sparse Columns?
A sparse column is another tool used to reduce the
amount of physical storage used in a database. They are the ordinary columns
that have an optimized storage for null values. Sparse columns reduce the space
requirements for null values at the cost of more overhead to retrieve nonnull
values
60. What
does TOP Operator Do?
The TOP operator is used to specify the number of
rows to be returned by a query. The TOP operator has new addition in SQL SERVER
2008 that it accepts variables as well as literal values and can be used with
INSERT, UPDATE, and DELETES statements.
61. What is
CTE?
CTE is an abbreviation Common Table Expression. A
Common Table Expression (CTE) is an expression that can be thought of as a
temporary result set which is defined within the execution of a single SQL
statement. A CTE is similar to a derived table in that it is not stored as an
object and lasts only for the duration of the query.
62. What is
MERGE Statement?
MERGE is a new feature that provides an efficient
way to perform multiple DML operations. In previous versions of SQL Server, we
had to write separate statements to INSERT, UPDATE, or DELETE data based on
certain conditions, but now, using MERGE statement we can include the logic of
such data modifications in one statement that even checks when the data is
matched then just update it and when unmatched then insert it. One of the most
important advantages of MERGE statement is all the data is read and processed
only once.
63. What is
Filtered Index?
Filtered Index is used to index a portion of rows
in a table that means it applies filter on INDEX which improves query
performance, reduce index maintenance costs, and reduce index storage costs
compared with full-table indexes. When we see an Index created with some where
clause then that is actually a FILTERED INDEX.
64. Which
are new data types introduced in SQL SERVER 2008?
- The GEOMETRY Type: The GEOMETRY data type is a system .NET
common language runtime (CLR) data type in SQL Server. This type
represents data in a two-dimensional Euclidean coordinate system.
- The GEOGRAPHY Type: The GEOGRAPHY datatype’s functions are the
same as with GEOMETRY. The difference between the two is that when you
specify GEOGRAPHY, you are usually specifying points in terms of latitude
and longitude.
- New Date and Time Datatypes: SQL
Server 2008 introduces four new datatypes related to date and time: DATE,
TIME, DATETIMEOFFSET, and DATETIME2.
- DATE: The
new DATE type just stores the date itself. It is based on the Gregorian
calendar and handles years from 1 to 9999.
- TIME: The
new TIME (n) type stores time with a range of 00:00:00.0000000 through
23:59:59.9999999. The precision is allowed with this type. TIME supports
seconds down to 100 nanoseconds. The n in TIME (n) defines this level of
fractional second precision, from 0 to 7 digits of precision.
- The DATETIMEOFFSET Type: DATETIMEOFFSET
(n) is the time-zone-aware version of a datetime datatype. The name will
appear less odd when you consider what it really is: a date + a time + a
time-zone offset. The offset is based on how far behind or ahead you are
from Coordinated Universal Time (UTC) time.
- The DATETIME2 Type: It
is an extension of the datetime type in earlier versions of SQL Server.
This new datatype has a date range covering dates from January 1 of year
1 through December 31 of year 9999. This is a definite improvement over
the 1753 lower boundary of the datetime datatype. DATETIME2 not only
includes the larger date range, but also has a timestamp and the same
fractional precision that TIME type provides
65. What
are the Advantages of using CTE?
- Using CTE improves the readability and makes maintenance of complex
queries easy.
- The query can be divided into separate, simple, logical building
blocks which can be then used to build more complex CTEs until final
result set is generated.
- CTE can be defined in functions, stored procedures, triggers or
even views.
- After a CTE is defined, it can be used as a Table or a View and can
SELECT, INSERT, UPDATE or DELETE Data.
66. What is
CLR?
In SQL Server 2008, SQL Server objects such as
user-defined functions can be created using such CLR languages. This CLR
language support extends not only to user-defined functions, but also to stored
procedures and triggers. You can develop such CLR add-ons to SQL Server using
Visual Studio 2008.
67. What
are synonyms?
Synonyms give you the ability to provide alternate
names for database objects. You can alias object names; for example, using the
Employee table as Emp. You can also shorten names. This is especially useful
when dealing with three and four part names; for example, shortening
server.database.owner.object to object.
68. What is
LINQ?
Language Integrated Query (LINQ) adds the ability
to query objects using .NET languages. The LINQ to SQL object/relational
mapping (O/RM) framework provides the following basic features:
- Tools to create classes (usually called entities) mapped to
database tables
- Compatibility with LINQ's standard query operations
- The DataContext class, with features such as entity record
monitoring, automatic SQL statement generation, record concurrency
detection, and much more
69. What is
Isolation Levels?
Transactions specify an isolation level that
defines the degree to which one transaction must be isolated from resource or
data modifications made by other transactions. Isolation levels are described
in terms of which concurrency side-effects, such as dirty reads or phantom
reads, are allowed.
Transaction isolation levels control:
- Whether locks are taken when data is read, and what type of locks
are requested.
- How long the read locks are held.
- Whether a read operation referencing rows modified by another
transaction:
- Blocks until the exclusive lock on the row is
freed.
- Retrieves the committed version of the row
that existed at the time the statement or transaction started.
- Reads the uncommitted data modification.
70. What is
use of EXCEPT Clause?
EXCEPT clause is similar to MINUS operation in
Oracle. The EXCEPT query and MINUS query returns all rows in the first query
that are not returned in the second query. Each SQL statement within the EXCEPT
query and MINUS query must have the same number of fields in the result sets
with similar data types.
71. How
would you handle error in SQL SERVER 2008?
SQL Server now supports the use of TRY...CATCH con
handling. TRY...CATCH lets us build error handling at the level we need, in the
way w to, by setting a region where if any error occurs, it will break out of
the region and head to an error handler.
The basic structure is as follows:
BEGIN TRY
stmts..
END TRY
BEGIN CATCH
stmts..
END CATCH
72. What is
RAISEERROR?
RaiseError generates an error message and initiates
error processing for the session. RAISERROR can either reference a user-defined
message stored in the sys.messages catalog view or build a message dynamically.
The message is returned as a server error message to the calling application or
to an associated CATCH block of a TRY | CATCH construct.
73. How to
rebuild Master Database?
Master database is system database and it contains
information about running server's configuration. When SQL Server 2005 is
installed it usually creates master, model, msdb, tempdb resource and
distribution system database by default. Only Master database is th one which
is absolutely must have database. Without Master database SQL Server cannot be
started. This is the reason it is extremely important to backup Master
database.
To rebuild the Master database, Run Setup.exe,
verify, and repair a SQL Server instance, and rebuild the system databases.
This procedure is most often used to rebuild the master database for a
corrupted installation of SQL Server.
74. What is
XML Datatype?
The xml data type lets you store XML documents and
fragments in a SQL Server database. An XML fragment is an XML instance that is
missing a single top-level element. You can create columns and variables of the
xml type and store XML instances in them. The xml data type and associated
methods help integrate XML into the relational framework of S Server.
75. What is
Data Compression?
In SQL SERVE 2008 Data Compression comes in two
flavors:
- Row Compression: Row
compression changes the format of physical storage of data. It minimize
the metadata (column information, length, offsets etc) associated with
each record. Numeric data types and fixed length strings are stored in
variable-length storage format, just like Varchar.
- Page Compression: Page
compression allows common data to be shared between rows for a given page.
Its uses the following techniques to compress data:
- Row compression.
- Prefix Compression. For every column in a
page duplicate prefixes are identified. These prefixes are saved in
compression information headers (CI) which resides after page header. A
reference number is assigned to these prefixes and that reference number
is replaced where ever those prefixes are being used.
- Dictionary Compression:
Dictionary compression searches for duplicate values throughout the page
and stores them in CI. The main difference between prefix and dictionary
compression is that prefix is only restricted to one column while
dictionary is applicable to the complete page.
76. What is
Catalogue Views?
Catalogue views return information that is used by
the SQL Server Database Engine. Catalogue Views are the most general interface
to the catalogue metadata and provide the most efficient way to obtain,
transform, and present customized forms of this information. All user-
available catalogue metadata is exposed through catalogue views.
77. What is
PIVOT and UNPIVOT?
A Pivot Table can automatically sort, count,
and total the data stored in one table or spreadsheet and create a second table
displaying the summarized data. The PIVOT operator turns the values of a
specified column into column names, effectively rotating a table.
UNPIVOT table is reverse of
PIVOT Table
78. What is
Dirty Read ?
A dirty read occurs when two operations say, read
and write occurs together giving the incorrect or unedited data. Suppose, A has
changed a row, but has not committed the changes. B reads the uncommitted data
but his view of the data may be wrong so that is Dirty Read.
79. What is
Aggregate Functions?
Aggregate functions perform a calculation on a set
of values and return a single value. Aggregate functions ignore NULL values
except COUNT function. HAVING clause is used, along with GROUP BY, for
filtering query using aggregate values.
Following functions are aggregate functions.
AVG, MIN CHECKSUM_AGG, SUM, COUNT, STDEV, COUNT_BIG, STDEVP, GROUPING, VAR, MAX. VARP
80. What do
you mean by Table Sample?
TABLESAMPLE allows you to extract a sampling of
rows from a table in the FROM clause. The rows retrieved are random and they
are not in any order. This sampling can be based on a percentage of number of
rows. You can use TABLESAMPLE when only a sampling of rows is necessary for the
application instead of a full result set.
81. What is
the difference between UNION and UNION ALL?
- UNION The
UNION command is used to select related information from two tables, much
like the JOIN command. However, when using the UNION command all selected
columns need to be of the same data type. With UNION, only distinct values
are selected.
- UNION ALL The
UNION ALL command is equal to the UNION command, except that UNION ALL
selects all values.
The difference between Union and Union all is that
Union all will not eliminate duplicate rows, instead it just pulls all rows
from all tables fitting your query specifics and combines them into a table.
82. What is
B-Tree?
The database server uses a B-tree structure to
organize index information. B-Tree generally has following types of index pages
or nodes:
- root node: A root node contains node pointers to branch
nodes which can be only one.
- branch node: A branch node contains pointers to leaf nodes
or other branch nodes which can be two or more.
- leaf nodes: A leaf node contains index items and
orizantal pointers to other leaf nodes which can be many.
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