SQL Interview Questions with Answers
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.
What is normalization?
Database normalization is a data design and organization process applied
to data structures based on
rules that help build relational databases. In relational database
design, the process of organizing data
to minimize redundancy. 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.
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
4NF: Isolate Independent Multiple Relationships
No table may contain two or more 1:n or n:m relationships that are not
5NF: Isolate Semantically Related Multiple Relationships
There may be practical constrains on information that justify separating
logically related many-to-many
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.
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.
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.
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;
the 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
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.
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
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.
Clustered indexes define the physical sorting of a database table’s rows
in the storage media. For this
reason, each database table may have only one clustered index.
Non-clustered indexes are created outside of the database table and
contain a sorted list of references
to the table itself.
What is the difference between clustered and a
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 nonclustered 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 nonclustered
index does not consist of
the data pages. Instead, the leaf nodes contain index rows.
What are the different index configurations a table
A table can have one of the following index configurations:
A clustered index
A clustered index and many nonclustered indexes
A nonclustered index
Many nonclustered indexes
What is cursors?
is a database object used by applications to manipulate data in a set on a
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
Fetch row from the cursor
Process fetched row
What is the use of DBCC commands?
DBCC stands for database consistency checker. We use these commands to
check the consistency of
the databases, i.e., maintenance, validation task and status checks.
E.g. DBCC CHECKDB - Ensures that tables in the db and the indexes are
DBCC CHECKALLOC - To check that all pages in a db are correctly
DBCC CHECKFILEGROUP - Checks all tables file group for any damage.
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.
Storped Procedure sp_addlinkedserver, sp_addlinkedsrvlogin will be used
add new Linked Server.
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 casesensitivity,
accent marks, kana character types and character width.
What are different type of Collation Sensitivity?
A and a, B and b, etc.
a and á, o and ó, etc.
When Japanese kana characters Hiragana and Katakana are treated
differently, it is called Kana
When a single-byte character (half-width) and the same character when
represented as a double-byte
character (full-width) are treated differently then it is width
What's the difference between a primary key and a
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.
How to implement one-to-one, one-to-many and
many-to-many relationships while
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.
What is a NOLOCK?
Using the NOLOCK query optimiser hint is generally considered good
practice in order to improve
concurrency on a busy system. When the NOLOCK hint is included in a
SELECT statement, no locks are
taken when data is read. The result is a Dirty Read, which means that
another process could be
updating the data at the exact time you are reading it. There are no
guarantees that your query will
retrieve the most recent data. The advantage to performance is that your
reading of data will not block
updates from taking place, and updates will not block your reading of
data. SELECT statements take
Shared (Read) locks. This means that multiple SELECT statements are
allowed simultaneous access, but
other processes are blocked from modifying the data. The updates will
queue until all the reads have
completed, and reads requested after the update will wait for the
updates to complete. The result to
your system is delay(blocking).
What is difference between DELETE & TRUNCATE
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 is faster and uses fewer system and transaction log resources
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 and its
columns, constraints, indexes
and so on remain. 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
Because TRUNCATE TABLE is not logged, it cannot activate a trigger.
TRUNCATE can not be Rolled back.
TRUNCATE is DDL Command.
TRUNCATE Resets identity of the table.
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.
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 though of as views that take parameters and can be
used in JOINs and other
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
What types of Joins are possible with Sql Server?
are used in queries to explain how different tables are related. Joins also let
you select data from
a table depending upon data from another table.
Types of joins: INNER JOINs, OUTER JOINs, CROSS JOINs. OUTER JOINs are
further classified as LEFT
OUTER JOINS, RIGHT OUTER JOINS and FULL OUTER JOINS.
What is the difference between a HAVING CLAUSE and a
Specifies a search condition for a group or an aggregate. 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. WHERE Clause is applied to each row before they are part of the
GROUP BY function in a query.
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 result
set. 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.
Properties of Sub-Query
A subquery must be enclosed in the parenthesis.
A subquery must be put in the right hand of the comparison operator, and
A subquery cannot contain a ORDER-BY clause.
A query can contain more than one sub-queries.
What are types of sub-queries?
subquery, where the subquery returns only one row.
Multiple-row subquery, where the subquery returns multiple rows,.and
Multiple column subquery, where the subquery returns multiple columns.
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 performance 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.
What is User Defined Functions?
User-Defined Functions allow to define its own T-SQL functions that can
accept 0 or more parameters
and return a single scalar data value or a table data type.
What kind of User-Defined Functions can be created?
There are three types of User-Defined functions in SQL Server 2000 and
they are Scalar, Inline Table-
Valued and Multi-statement Table-valued.
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
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
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.
Which TCP/IP port does SQL Server run on? How can it
SQL Server runs on port 1433. It can be changed from the Network Utility
TCP/IP properties –> Port
number.both on client and the server.
What are the authentication modes in SQL Server? How can
it be changed?
Windows mode and mixed mode (SQL & 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
Where are SQL server users names and passwords are
stored in sql server?
They get stored in master db in the sysxlogins table.
command using Query Analyzer will give you the version of SQL server and
SELECT SERVERPROPERTY('productversion'), SERVERPROPERTY
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.
a stored procedure call itself or recursive stored procedure? How many level SP
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.
The @@ERROR automatic variable returns the error code of the last
Transact-SQL statement. If there
was no error, @@ERROR returns zero. Because @@ERROR is reset after each
it must be saved to a variable if it is needed to process it further
after checking it.
Stored procedures report errors to client applications via the RAISERROR
doesn't change the flow of a procedure; it merely displays an error
message, sets the @@ERROR
automatic variable, and optionally writes the message to the SQL Server
error log and the NT
application event log.
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
can be used this as the Disaster Recovery plan. The key feature of log
shipping is that is will
automatically backup transaction logs throughout the day and
automatically restore them on the
standby server at defined interval.
is the difference between a local and a global variable?
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 are 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.
What command do we use to rename a db?
sp_renamedb ‘oldname’ , ‘newname’
If someone is using db it will not accept sp_renmaedb. In that case
first bring db to single user using
sp_dboptions. Use sp_renamedb to rename database. Use sp_dboptions to
bring database to multi user
What is sp_configure commands and set commands?
Use sp_configure to display or change server-level settings. To change
database-level settings, use
ALTER DATABASE. To change settings that affect only the current user
session, use the SET statement.
are the different types of replication? Explain.
The SQL Server 2000-supported replication types are as follows:
Snapshot replication distributes data exactly as it appears at a
specific moment in time and does not
monitor for updates to the data. Snapshot replication is best used as a
method for replicating data that
changes infrequently or where the most up-to-date values (low latency)
are not a requirement. When
synchronization occurs, the entire snapshot is generated and sent to
Transactional replication, an initial snapshot of data is applied at
Subscribers, and then when data
modifications are made at the Publisher, the individual transactions are
captured and propagated to
Merge replication is the process of distributing data from Publisher to
Subscribers, allowing the
Publisher and Subscribers to make updates while connected or
disconnected, and then merging the
updates between sites when they are connected.
are the OS services that the SQL Server installation adds?
MS SQL SERVER SERVICE, SQL AGENT SERVICE, DTC (Distribution transac
are three SQL keywords used to change or set someone’s permissions?
GRANT, DENY, and REVOKE.
does it mean to have quoted_identifier on? What are the implications of having
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.
is the STUFF function and how does it differ from the REPLACE function?
STUFF function to overwrite existing characters. Using this syntax,
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
REPLACE function to replace existing characters of all occurance. Using
REPLACE(string_expression, search_string, replacement_string), where
every incidence of
search_string found in the string_expression will be replaced with
query analyzer, 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 <
to rebuild Master Database?
Shutdown Microsoft SQL Server 2000, and then run Rebuildm.exe. This is
located in the Program
Files\Microsoft SQL Server\80\Tools\Binn directory.
In the Rebuild Master dialog box, click Browse.
In the Browse for Folder dialog box, select the \Data folder on the SQL
Server 2000 compact disc or in
the shared network directory from which SQL Server 2000 was installed,
and then click OK.
Click Settings. In the Collation Settings dialog box, verify or change
settings used for the master
database and all other databases.
Initially, the default collation settings are shown, but these may not
match the collation selected during
setup. You can select the same settings used during setup or select new
collation settings. When done,
In the Rebuild Master dialog box, click Rebuild to start the process.
The Rebuild Master utility reinstalls the master database.
To continue, you may need to stop a server that is running.
is the basic functions for master, msdb, model, tempdb databases?
The Master database holds information for all databases located on the
SQL Server instance and is the
glue that holds the engine together. Because SQL Server cannot start
without a functioning master
database, 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
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
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
is data integrity? Explain constraints?
Data integrity is an important feature in SQL Server. When used
properly, it ensures that data is
accurate, correct, and valid. It also acts as a trap for otherwise
undetectable bugs within applications.
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
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
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
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.
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.
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.
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.
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
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 controled. Identity/GUID columns do not need
to be indexed.
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
What is a table called, if it does not have 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
Unindexed tables are good for fast storing of data. Many times it is
better to drop all indexes from table
and than do bulk of inserts and to restore those indexes after that.
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.
do you load large data to the SQL server database?
BulkCopy is a tool used to copy huge amount of data from tables. BULK
INSERT command helps to
Imports a data file into a database table or view in a user-specified
we rewrite subqueries into simple select statements or with joins?
Subqueries can often be re-written to use a standard outer join,
resulting in faster performance. As we
may know, an outer join uses the plus sign (+) operator to tell the
database to return all non-matching
rows with NULL values. Hence we combine the outer join with a NULL test
in the WHERE clause to
reproduce the result set without using a sub-query.
SQL Servers linked to other servers like Oracle?
SQL Server can be lined to any server provided it has OLE-DB provider
from Microsoft to allow a link.
E.g. Oracle has a OLE-DB provider for oracle that Microsoft provides to
add it as linked server to SQL Server group.
to know which index a table is using?
SELECT table_name,index_name FROM user_constraints
to copy the tables, schema and views from one SQL server to another?
Microsoft SQL Server 2000 Data Transformation Services (DTS) is a set of
graphical tools and
programmable objects that lets user extract, transform, and consolidate
data from disparate sources
into single or multiple destinations.
What is 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 have a hierarchal
reporting structure whereby one member of staff reports to another.
is 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.
virtual table does a trigger use?
Inserted and Deleted.
List few advantages of Stored Procedure.
· 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
· Stored procedures provide better security to your
· 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
· 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
· Integrated, meaning that the database contains data
from most or all of an organization's
operational applications, and that this data is made consistent.
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
do SQL server 2000 and XML linked? Can XML be used to access data?
FOR XML (ROW, AUTO, EXPLICIT)
You can execute SQL queries against existing relational databases to
return results as XML rather than
standard rowsets. These queries can be executed directly or from within
stored procedures. To retrieve
XML results, use the FOR XML clause of the SELECT statement and specify
an XML mode of RAW, AUTO,
OPENXML is a Transact-SQL keyword that provides a relational/rowset view
over an in-memory XML
document. OPENXML is a rowset provider similar to a table or a view.
OPENXML provides a way to
access XML data within the Transact-SQL context by transferring data
from an XML document into the
relational tables. Thus, OPENXML allows you to manage an XML document
and its interaction with the
is an execution plan? When would you use it? How would you view the execution
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.