SQL - Normalization

What is Normalization?

Normalization is the process of efficiently organizing data in a database. There are two goals of the normalization process: eliminating redundant data (for example, storing the same data in more than one table) and ensuring data dependencies make sense (only storing related data in a table). Both of these are worthy goals as they reduce the amount of space a database consumes and ensure that data is logically stored.

The Normal Forms

The database community has developed a series of guidelines for ensuring that databases are normalized. These are referred to as normal forms and are numbered from one (the lowest form of normalization, referred to as first normal form or 1NF) through five (fifth normal form or 5NF). In practical applications, you'll often see 1NF, 2NF, and 3NF along with the occasional 4NF. Fifth normal form is very rarely seen and won't be discussed in this article.

Before we begin our discussion of the normal forms, it's important to point out that they are guidelines and guidelines only. Occasionally, it becomes necessary to stray from them to meet practical business requirements. However, when variations take place, it's extremely important to evaluate any possible ramifications they could have on your system and account for possible inconsistencies. That said, let's explore the normal forms.

First Normal Form (1NF)

First normal form (1NF) sets the very basic rules for an organized database:

• Eliminate duplicative columns from the same table.
• Create separate tables for each group of related data and identify each row with a unique column or set of columns (the primary key).

Second Normal Form (2NF)

Second normal form (2NF) further addresses the concept of removing duplicative data:

• Meet all the requirements of the first normal form.
• Remove subsets of data that apply to multiple rows of a table and place them in separate tables.
• Create relationships between these new tables and their predecessors through the use of foreign keys.

Third Normal Form (3NF)

Third normal form (3NF) goes one large step further:

• Meet all the requirements of the second normal form.
• Remove columns that are not dependent upon the primary key.

Fourth Normal Form (4NF)

Finally, fourth normal form (4NF) has one additional requirement:

• Meet all the requirements of the third normal form.
• A relation is in 4NF if it has no multi-valued dependencies.

Remember, these normalization guidelines are cumulative. For a database to be in 2NF, it must first fulfill all the criteria of a 1NF database.

Source ::  http://databases.about.com/od/specificproducts/a/normalization.htm

SQL QA's

What the difference between UNION and UNIONALL?
Union will remove the duplicate rows from the result set while Union all does'nt.

What is the difference between TRUNCATE and DELETE commands?
Both will result in deleting all the rows in the table .TRUNCATE call cannot be rolled back as it is a DDL command and all memory space for that table is released back to the server. TRUNCATE is much faster.Whereas DELETE call is an DML command and can be rolled back.

Which system table contains information on constraints on all the tables created ?
yes,
USER_CONSTRAINTS,
system table contains information on constraints on all the tables created

Explain normalization ? Normalisation means refining the redundancy and maintain stablisation. there are four types of normalisation :
first normal forms, second normal forms, third normal forms and fourth Normal forms.

How to find out the database name from SQL*PLUS command prompt?Select * from global_name;
This will give the datbase name which u r currently connected to.....

What is the difference between SQL and SQL Server ?
SQLServer is an RDBMS just like oracle,DB2 from Microsoft
whereas
Structured Query Language (SQL), pronounced "sequel", is a language that provides an interface to relational database systems. It was developed by IBM in the 1970s for use in System R. SQL is a de facto standard, as well as an ISO and ANSI standard. SQL is used to perform various operations on RDBMS.

What is diffrence between Co-related sub query and nested sub query?
Correlated subquery runs once for each row selected by the outer query. It contains a reference to a value from the row selected by the outer query.
Nested subquery runs only once for the entire nesting (outer) query. It does not contain any reference to the outer query row.
For example,
Correlated Subquery:
select e1.empname, e1.basicsal, e1.deptno from emp e1 where e1.basicsal = (select max(basicsal) from emp e2 where e2.deptno = e1.deptno)
Nested Subquery:
select empname, basicsal, deptno from emp where (deptno, basicsal) in (select deptno, max(basicsal) from emp group by deptno)

WHAT OPERATOR PERFORMS PATTERN MATCHING?
Pattern matching operator is LIKE and it has to used with two attributes
1. % and
2. _ ( underscore )
% means matches zero or more characters and under score means mathing exactly one character

What is database?
A database is a collection of data that is organized so that itscontents can easily be accessed, managed and updated.

What is cluster.cluster index and non cluster index ? Clustered Index:- A Clustered index is a special type of index that reorders the way records in the table are physically stored. Therefore table may have only one clustered index.Non-Clustered Index:- 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 in the disk. The leaf nodes of a non-clustered index does not consists of the data pages. instead the leaf node contains index rows.

How can i hide a particular table name of our schema?you can hide the table name by creating synonyms.
e.g) you can create a synonym y for table x
create synonym y for x;

What is difference between DBMS and RDBMS?
The main difference of DBMS & RDBMS is

RDBMS have Normalization. Normalization means to refining the redundant and maintain the stablization.
the DBMS hasn't normalization concept.
What are the advantages and disadvantages of primary key and foreign key in SQL?

Primary key
Advantages
1) It is a unique key on which all the other candidate keys are functionally dependent
Disadvantage
1) There can be more than one keys on which all the other attributes are dependent on.

Foreign Key
Advantage
1)It allows refrencing another table using the primary key for the other table
Which date function is used to find the difference between two dates?
datediff
for Eg: select datediff (dd,'2-06-2007','7-06-2007')
output is 5

Ref : http://faq.programmerworld.net/database/sql-interview-questions-and-answers.html

UDF & Stored Procedures in SQL Server

User Defined Functions Stored Procedures

1 UDF are simpler to invoke than Stored Procedures from inside another SQL statement. They are Complex to Invoke.

2 SQL functions that return non-deterministic values are not allowed to be called from inside User Defined Functions. GETDATE is an example of a non-deterministic function. Every time the function is called, a different value is returned. Therefore, GETDATE cannot be called from inside a UDF you create, but could not be used inside the function itself. Non-deterministic values are not allowed to be called from inside Stored Procedure.

3 The User Defined Function must be prefaced with the owner name, DBO in this case. Not mandatory.

4 When call function then the parameter must transmit full.
Ex:
CREATE FUNCTION ftest(@val01 varchar(10),@val02 varchar(10) )
CREATE PROCEDURE pTest(
@val01 varchar(10) = ‘10',
@val02 varchar(10) = NULL
)
Call:
dbo.ftest(@val01,@val02) —-> OK
dbo.ftest(@val01) —-> NOT OK
When call store procedure then the parameter allow empty.
CREATE PROCEDURE pTest(
@val01 varchar(10) = ‘10',
@val02 varchar(10) = NULL
)
Call:
dbo.ftest(@val01,@val02) —-> OK
dbo.ftest(@val01) —-> NOT OK
pTest(@val01,@val02) —-> OK
pTest(@val01) —-> OK

5 A UDF is always used to return a value or a table object. You can also get values back from a stored procedure by the return code (integer only) or an output parameter.

6 Function return type could be scalar or table or table values(SQL Server). Stored procedure returns always integer value by default zero.

7 Stored Procedure is pre compiled execution plan Functions are not precompiled.
8 Function returns only one value at a time. Stored Procedure returns more than one value at a time.
9 We can call the functions in SQL statements (select max(sal) from emp). We cannot call Stored Procedures in SQL Statements.
10 Function do not return the images, text. Stored Procedure returns all.
11 Functions are used for computations. Procedures can be used for performing business logic.
12 Functions MUST return a value. Procedures need not be.
13 Function parameters are always IN, no OUT is possible Stored procedures can have input and output parameters, while user defined functions only can have input parameters. Output parameters must be returned as return values.
14 UDF can be used in the SQL Statements anywhere in the WHERE/HAVING/SELECT section Stored procedures cannot be.
15 If you have an operation such as a query with a FROM clause that requires a rowset be drawn from a table or set of tables, then a function will be your appropriate choice. However, when you want to use that same rowset in your application the better choice would be a stored procedure.
16 Easy to create a function. Skill Expertise is required to create a stored Procedure.

SQL Server QA's - V

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 Scalar, Inline Table-Valued and 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 T-SQL 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.

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.

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'),

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.

Can a stored procedure call itself or recursive stored procedure? How many level SP nesting 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.

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 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.

SQL Server QA's - IV

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.

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.

Using query analyzer, name 3 ways to get an accurate count of the number of records in a table?
SELECT *FROM table1SELECT COUNT(*)FROM table1SELECT rowsFROM sysindexesWHERE id = OBJECT_ID(table1)
AND indid < 2
How to rebuild Master Database?
Shutdown Microsoft SQL Server 2000, and then run Rebuildm.exe. This is located in the Program Files\Microsoft SQL Server\80\Tools\Binn directory.
In the Rebuild Master dialog box, click Browse.
In the Browse for Folder dialog box, select the \Data folder on the SQL Server 2000 compact disc or in the shared network directory from which SQL Server 2000 was installed, and then click OK.
Click Settings. In the Collation Settings dialog box, verify or change settings used for the master database and all other databases.
Initially, the default collation settings are shown, but these may not match the collation selected during setup. You can select the same settings used during setup or select new collation settings. When done, click OK.
In the Rebuild Master dialog box, click Rebuild to start the process.
The Rebuild Master utility reinstalls the master database.
To continue, you may need to stop a server that is running.

Source: http://msdn2.microsoft.com/en-us/library/aa197950(SQL.80).aspx

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 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.

Source : http://blog.sqlauthority.com/2007/04/18/sql-server-interview-questions/

SQL Server QA's - III

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 using logs.
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 using logs.
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. HAVING criteria is applied after the the grouping of rows has occurred.

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.

SQL Server -QA's - Part II

What is normalization? - Well a relational database is basically composed of tables that contain related data. So the Process of organizing this data into tables is actually referred to as normalization.

What is a Stored Procedure? - Its nothing but a set of T-SQL statements combined to perform a single task of several tasks. Its basically like a Macro so when you invoke the Stored procedure, you actually run a set of statements.

Can you give an example of Stored Procedure? - sp_helpdb , sp_who2, sp_renamedb are a set of system defined stored procedures. We can also have user defined stored procedures which can be called in similar way.

What is a trigger? - Triggers are basically used to implement business rules. Triggers is also similar to stored procedures. The difference is that it can be activated when data is added or edited or deleted from a table in a database.

What is a view? - If we have several tables in a db and we want to view only specific columns from specific tables we can go for views. It would also suffice the needs of security some times allowing specfic users to see only specific columns based on the permission that we can configure on the view. Views also reduce the effort that is required for writing queries to access specific columns every time.

What is an Index? - When queries are run against a db, an index on that db basically helps in the way the data is sorted to process the query for faster and data retrievals are much faster when we have an index.

What are the types of indexes available with SQL Server? - There are basically two types of indexes that we use with the SQL Server. Clustered and the Non-Clustered.

What is the basic difference between clustered and a non-clustered index? - The difference is that, Clustered index is unique for any given table and we can have only one clustered index on a table. The leaf level of a clustered index is the actual data and the data is resorted in case of clustered index. Whereas in case of non-clustered index the leaf level is actually a pointer to the data in rows so we can have as many non-clustered indexes as we can on the db.

What are cursors? - Well cursors help us to do an operation on a set of data that we retreive by commands such as Select columns from table. For example : If we have duplicate records in a table we can remove it by declaring a cursor which would check the records during retreival one by one and remove rows which have duplicate values.

When do we use the UPDATE_STATISTICS command? - This command is basically used when we do a large processing of data. If we do a large amount of deletions any modification or Bulk Copy into the tables, we need to basically update the indexes to take these changes into account. UPDATE_STATISTICS updates the indexes on these tables accordingly.

Which TCP/IP port does SQL Server run on? - SQL Server runs on port 1433 but we can also change it for better security.

From where can you change the default port? - From the Network Utility TCP/IP properties –> Port number.both on client and the server.

Can you tell me the 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.

Can we use Truncate command on a table which is referenced by FOREIGN KEY? - No. We cannot use Truncate command on a table with Foreign Key because of referential integrity.

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.

Can you give me some DBCC command options?(Database consistency check) - DBCC CHECKDB - Ensures that tables in the db and the indexes are correctly linked.and DBCC CHECKALLOC - To check that all pages in a db are correctly allocated. DBCC SQLPERF - It gives report on current usage of transaction log in percentage. DBCC CHECKFILEGROUP - Checks all tables file group for any damage.

What command do we use to rename a db? - sp_renamedb ‘oldname’ , ‘newname’

Well sometimes sp_reanmedb may not work you know because if some one is using the db it will not accept this command so what do you think you can do in such cases? - In such cases we can first bring to db to single user using sp_dboptions and then we can rename that db and then we can rerun the sp_dboptions command to remove the single user mode.

What is the difference between a HAVING CLAUSE and 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 do you mean by COLLATION? - Collation is basically the sort order. There are three types of sort order Dictionary case sensitive, Dictonary - case insensitive and Binary.

What is a Join in SQL Server? - Join actually puts data from two or more tables into a single result set.

Can you explain the types of Joins that we can have with Sql Server? - There are three types of joins: Inner Join, Outer Join, Cross Join

When do you use SQL Profiler? - SQL Profiler utility allows us to basically track connections to the SQL Server and also determine activities such as which SQL Scripts are running, failed jobs etc..

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.

Can you link only other SQL Servers or any database servers such as Oracle? - We can link any server provided we have the OLE-DB provider from Microsoft to allow a link. For Oracle we have a OLE-DB provider for oracle that microsoft provides to add it as a linked server to the sql server group.

Which stored procedure will you be running to add a linked server? - sp_addlinkedserver, sp_addlinkedsrvlogin

What are the OS services that the SQL Server installation adds? - MS SQL SERVER SERVICE, SQL AGENT SERVICE, DTC (Distribution transac co-ordinator)

Can you explain the role of each service? - SQL SERVER - is for running the databases SQL AGENT - is for automation such as Jobs, DB Maintanance, Backups DTC - Is for linking and connecting to other SQL Servers

How do you troubleshoot SQL Server if its running very slow? - First check the processor and memory usage to see that processor is not above 80% utilization and memory not above 40-45% utilization then check the disk utilization using Performance Monitor, Secondly, use SQL Profiler to check for the users and current SQL activities and jobs running which might be a problem. Third would be to run UPDATE_STATISTICS command to update the indexes

Lets say due to N/W or Security issues client is not able to connect to server or vice versa. How do you troubleshoot? - First I will look to ensure that port settings are proper on server and client Network utility for connections. ODBC is properly configured at client end for connection ——Makepipe & readpipe are utilities to check for connection. Makepipe is run on Server and readpipe on client to check for any connection issues.

What are the authentication modes in SQL Server? - Windows mode and mixed mode (SQL & Windows).

Where do you think the users names and passwords will be stored in sql server? - They get stored in master db in the sysxlogins table.

What is log shipping? Can we do logshipping with SQL Server 7.0 - Logshipping is a new feature of SQL Server 2000. We should have two SQL Server - Enterprise Editions. From Enterprise Manager we can configure the logshipping. In logshipping 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 we can use this as the DR (disaster recovery) plan.

Let us say the SQL Server crashed and you are rebuilding the databases including the master database what procedure to you follow? - For restoring the master db we have to stop the SQL Server first and then from command line we can type SQLSERVER –m which will basically bring it into the maintenance mode after which we can restore the master db.

Let us say master db itself has no backup. Now you have to rebuild the db so what kind of action do you take? - (I am not sure- but I think we have a command to do it).

What is BCP? When do we use it? - BulkCopy is a tool used to copy huge amount of data from tables and views. But it won’t copy the structures of the same.

What should we do to copy the tables, schema and views from one SQL Server to another? - We have to write some DTS packages for it.

SQL Server

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:

No indexes

A clustered index

A clustered index and many nonclustered indexes

A nonclustered index

Many nonclustered indexes

What is cursors?

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:

Declare cursor

Open cursor

Fetch row from the cursor

Process fetched row

Close cursor

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 case-sensitivity, 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 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.

Reference : Pinal Dave (http://blog.SQLAuthority.com)

DS - Dimensions

Altering Dimensions

You can modify a dimension using the ALTER DIMENSION statement. You can add ordrop a level, hierarchy, or attribute from the dimension using this command.Referring to the time dimension mentioned earlier, you can remove theattribute fis_year, drop the hierarchy fis_rollup, or remove the level fiscal_year. In addition, you can add a new level called f_year as in the following:ALTER DIMENSION times_dim DROP ATTRIBUTE fis_year;ALTER DIMENSION times_dim DROP HIERARCHY fis_rollup;ALTER DIMENSION times_dim DROP LEVEL fis_year;ALTER DIMENSION times_dim ADD LEVEL f_year IS times.fiscal_year;If you used the extended_attribute_clause when creating the dimension, youcan drop one attribute column without dropping all attribute columns. This isillustrated in "Dropping and Creating Attributes with Columns"...

Validating Dimensions 

The information of a dimension object is declarative only and not enforced by thedatabase. If the relationships described by the dimensions are incorrect, incorrectresults could occur. Therefore, you should verify the relationships specified byCREATE DIMENSION using the DBMS_DIMENSION.VALIDATE_DIMENSIONprocedure periodically.This procedure is easy to use and has only four parameters:

■ dimension: the owner and name.

■ incremental: set to TRUE to check only the new rows for tables of thisdimension.

■ check_nulls: set to TRUE to verify that all columns that are not in the levelscontaining a SKIP WHEN NULL clause are not null.

■ statement_id: a user-supplied unique identifier to identify the result of eachrun of the procedure.The following example validates the dimension TIME_FN in the sh schema:@utldim.sqlEXECUTE...

Viewing Dimensions 

Dimensions can be viewed through one of two methods:

■ Using Oracle Enterprise Manager

■ Using the DESCRIBE_DIMENSION ProcedureUsing Oracle Enterprise ManagerAll of the dimensions that exist in the data warehouse can be viewed using OracleEnterprise Manager. Select the Dimension object from within the Schema icon todisplay all of the dimensions. Select a specific dimension to graphically display itshierarchy, levels, and any attributes that have been defined.Using the DESCRIBE_DIMENSION ProcedureTo view the definition of a dimension, use the DESCRIBE_DIMENSION procedure inthe DBMS_DIMENSION package. For example, if a dimension is created in the shsample schema with the following statements:CREATE DIMENSION channels_dimLEVEL channel IS (channels.channel_id)LEVEL channel_class IS (channels.channel_class)HIERARCHY...

Creating Dimensions 

Before you can create a dimension object, the dimension tables must exist in thedatabase possibly containing the dimension data. For example, if you create acustomer dimension, one or more tables must exist that contain the city, state, andcountry information. In a star schema data warehouse, these dimension tables alreadyexist. It is therefore a simple task to identify which ones will be used.Now you can draw the hierarchies of a dimension as shown in Figure. Forexample, city is a child of state (because you can aggregate city-level data up tostate), and country. This hierarchical information will be stored in the database object dimension.In the case of normalized or partially normalized dimension representation (adimension that is stored in more than one table), identify how these tables...