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.
are the difference between clustered and a non-clustered index?
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.
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.
are the different index configurations a table can have?
A table can have one
of the following index configurations:
clustered index and many nonclustered indexes
are different types of Collation Sensitivity?
sensitivity - A and a, B and b,
Sensitivity - When Japanese kana
characters Hiragana and Katakana are treated differently, it is called Kana
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.
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.
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.
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 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
TRUNCATE is DDL
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 can be rolled
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 cannot
be rolled back but DELETE can be rolled back.
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.
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.
are the properties and different Types of Sub-Queries?
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.
where the sub-query returns only one row.
sub-query, where the sub-query returns multiple rows,. and
sub-query, where the sub-query returns multiple columns
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.
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.
command using Query Analyzer will give you the version of SQL server and
SERVERPROPERTY ('productversion'), SERVERPROPERTY ('productlevel'),
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 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.
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.
3 ways to get an accurate count of the number of records in a table?
* FROM table1
SELECT COUNT(*) FROM table1
SELECT rows FROM sysindexes WHERE id = OBJECT_ID(table1) AND indid < 2
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 difference between a Local and a Global temporary table?
local temporary table exists only for
the duration of a connection or, if defined inside a compound statement, for
the duration of the compound statement.
global temporary 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.
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.
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.
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.
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
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.
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.
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.
@RC = @@ROWCOUNT, @ER = @@ERROR
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.
are the advantages of using Stored Procedures?
Stored procedure can
reduced network traffic and latency, boosting application performance.
execution plans can be reused, staying cached in SQL Server's memory, reducing
Stored procedures help
promote code reuse.
Stored procedures can
encapsulate logic. You can change stored procedure code without affecting
provide better security to your data.
is a table called, if it has neither Cluster nor Non-cluster Index? What is it
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.
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.
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
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.
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.