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.
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