1.
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.
2.
What are the difference between clustered and a non-clustered index?
1.
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.
2.
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.
3.
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
4.
What are different types of Collation Sensitivity?
1.
Case sensitivity -
A and a, B and b, etc.
2.
Accent sensitivity
3.
Kana Sensitivity -
When Japanese kana characters Hiragana and Katakana are treated differently, it
is called Kana sensitive.
4.
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.
5.
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.
6.
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.
7.
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.
1.
TRUNCATE:
1.
TRUNCATE is faster and uses fewer
system and transaction log resources than DELETE.
2.
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.
3.
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.
4.
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.
5.
TRUNCATE cannot be rolled back.
6.
TRUNCATE is DDL Command.
7.
TRUNCATE Resets identity of the table
2.
DELETE:
1.
DELETE removes rows one at a time and
records an entry in the transaction log for each deleted row.
2.
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.
3.
DELETE Can be used with or without a
WHERE clause
4.
DELETE Activates Triggers.
5.
DELETE can be rolled back.
6.
DELETE is DML Command.
7.
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.
8.
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.
9.
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.
10.
What are the properties and different Types of Sub-Queries?
1.
Properties of
Sub-Query
1.
A sub-query must be enclosed in the
parenthesis.
2.
A sub-query must be put in the right
hand of the comparison operator, and
3.
A sub-query cannot contain an
ORDER-BY clause.
4.
A query can contain more than one
sub-query.
2.
Types of Sub-Query
1.
Single-row sub-query, where the
sub-query returns only one row.
2.
Multiple-row sub-query, where the
sub-query returns multiple rows,. and
3.
Multiple column sub-query, where the
sub-query returns multiple columns
11.
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.
12.
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.
13.
Which command using Query Analyzer will give you the version of SQL server and
operating system?
SELECT SERVERPROPERTY
('productversion'), SERVERPROPERTY ('productlevel'), SERVERPROPERTY
('edition').
14.
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.
15.
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.
16.
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.
17.
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
18.
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.
19.
What is the difference between a Local and a Global temporary table?
1.
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.
2.
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.
20.
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.
21.
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.
22.
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.
23.
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.
24.
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.
25.
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.
26.
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
27.
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.
28.
What are the advantages of using Stored Procedures?
1.
Stored procedure can reduced network
traffic and latency, boosting application performance.
2.
Stored procedure execution plans can
be reused, staying cached in SQL Server's memory, reducing server overhead.
3.
Stored procedures help promote code
reuse.
4.
Stored procedures can encapsulate
logic. You can change stored procedure code without affecting clients.
5.
Stored procedures provide better
security to your data.
29.
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.
30.
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.
31.
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.
32.
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.
33.
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.
