HI
Below content i am not prepared own, that content take from different sites for my interview preparation.
About SQL Server:
Microsoft SQL Server is a relational database management system
(RDBMS) produced by Microsoft. Its primary query language is Transact-SQL,
an implementation of the ANSI/ISO standard Structured Query Language (SQL)
used by both Microsoft and Sybase.Generically, any database management
system (DBMS) that can respond to queries from client machines formatted in
the SQL language.
SQL (Structured Query Language) is a standard interactive and programming
language for getting information from and updating a database. Although SQL
is both an ANSI and an ISO standard, many database products support SQL with
proprietary extensions to the standard language. Queries take the form of a
command language that lets you select, insert, update, find out the location of
data, and so forth. There is also a programming interface.
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.
What is the STUFF function and how does it differ from the REPLACE function?
STUFF function 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 occurance. Using this 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.
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 alues 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
Using query analyzer, name 3 ways to get an accurate count of the number of
records in atable?
SELECT * FROM table1
SELECT COUNT(*) FROM table1
SELECT rows FROM sysindexes WHERE id = OBJECT_ID(table1) AND indid < 2
What is Index in SQL Server?
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 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 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 can have?
A table can have one of the following index configurations:
1. No indexes
2. A clustered index
3. A clustered index and many nonclustered indexes
4. A nonclustered index
5. Many nonclustered indexes
What is Cursor in SQL Server?
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:
1. Declare cursor
2. Open cursor
3. Fetch row from the cursor
4. Process fetched row
5. Close cursor
6. Deallocate cursor
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
correctly linked. DBCC CHECKALLOC - To check that all pages in a db are
correctly allocated. 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?
Case sensitivity
A and a, B and b, etc.
Accent sensitivity
a and á, o and ó, etc.
Kana Sensitivity
When Japanese kana characters Hiragana and Katakana are treated differently,
it is called Kana sensitive.
Width sensitivity
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 sensitive.
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.
How to implement one-to-one, one-to-many and many-to-many relationships
whiledesigning 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.
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 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 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
constraint.
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
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 Rowset operations.
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.
What types of Joins are possible with Sql Server?
Joins 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 WHERE CLAUSE?
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?
Single-row 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
1. Scalar
2. Inline Table-Valued
3. 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 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.
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 –> Port number both on client and the server.
Can a stored procedure call itself or recursive stored procedure? How many
level SP nestingpossible?
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.
EXECUTE permission denied on object 'sp_name', database 'dbName'
GRANT EXECUTE ON sp_name TO user_name
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.
What are different Normalization Forms?
1NF: Eliminat 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: Eliminat Redundant Data
If an attribute depends on only part of a multi-valued key, remove it to a
separate table.
3NF: Eliminat 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: Isolat 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.
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 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 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.
What is Trigger?
A Stored Procedure is a named group of SQL statements that ha e 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 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.
What 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 entity integrity.
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.
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.
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.
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.
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.
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.
What is a table called, if it does not have neither Cluster nor Non-cluster
Index? What is itused 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 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.
How 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 format.
Can 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.
Can 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.
How to know which index a table is using?
SELECT table_name,index_name FROM user_constraints
How 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.
What 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.
Which 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 affecting clients.
· Stored procedures provide better security to your data.
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.
Where are SQL server users names and passwords are stored in sql server?
They get stored in master db in the sysxlogins table.
Which command using Query Analyzer will give you the version of SQL server
and operating system?
SELECT SERVERPROPERTY('productversion'), SERVERPROPERTY ('productlevel'),
SERVERPROPERTY ('edition')
What is @@ERROR?
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 Transact-SQL statement, it must be saved to a
variable if it is needed to process it further after checking it.
What is Raiseerror?
Stored procedures report errors to client applications via the RAISERROR
command. 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.
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 Security
page.
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.
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 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.
What 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 mode.
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.
What are the different types of replication? Explain.
The SQL Server 2000-supported replication types are as follows:
· Transactional
· Snapshot
· Merge
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 Subscribers.
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 Subscribers.
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.
What are the OS services that the SQL Server installation adds?
MS SQL SERVER SERVICE, SQL AGENT SERVICE, DTC (Distribution transac co-
ordinator)
What are three SQL keywords used to change or set someone’s permissions?
GRANT, DENY, and REVOKE.
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.
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.
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.
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.
Whar is an index? What are the types of indexes? How many clustered indexes
can be created on a table?
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.
what are the advantages and disadvantages, if you create a separate index on
each column of a 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.
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.
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.
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 Maximum Size of a Row?
8060 Bytes.
What are the 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.
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.
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.
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