What is @@rowcount and with small code snippet explain the
usage?
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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 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 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 DataWarehousing?
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 together;
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 reporting;
Integrated, meaning that the database contains data from
most or all of an organization’s operational applications,
and that this data is made consistent.
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.
How 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, or EXPLICIT.
OPENXML
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
relational environment.
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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