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1. What are different normalization forms?

1NF: Eliminate Repeating Groups Make a separate table for each set of related attributes, and give each table a primary key. 
Each field contains at most one value from its attribute domain. 
• 2NF: Eliminate Redundant Data If an attribute depends on only part of a multi-valued key, remove it to a separate table.
• 3NF: Eliminate Columns Not Dependent On Key If attributes do not contribute to a description of the key, remove them to a separate table. 
All attributes must be directly dependent on the primary key.
• BCNF: Boyce-Codd Normal Form If there are non-trivial dependencies between candidate key attributes, separate them out 
into distinct tables.
• 4NF: Isolate Independent Multiple Relationships No table may contain two or more 1:n or n:m relationships that are not directly related.
• 5NF: Isolate Semantically Related Multiple Relationships There may be practical constrains on information that justify separating logically related 
many-to-many relationships.
• ONF: Optimal Normal Form A model limited to only simple (elemental) facts, as expressed in Object Role Model notation.
• DKNF: Domain-Key Normal Form A model free from all modification anomalies is said to be in DKNF.

Remember, these normalization guidelines are cumulative. For a database to be in 3NF, it must first fulfill all the criteria of a 2NF and 1NF database.

2. What are different Types of Join?

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.
• Inner Join A join that displays only the rows that have a match in both joined tables is known as inner 
Join. This is the default type of join in the Query and View Designer.
• Outer Join A join that includes rows even if they do not have related rows in the joined table is an 
Outer Join. You can create three different outer join to specify the unmatched rows to be 
included:

• Left Outer Join: In Left Outer Join all rows in the first-named table i.e. "left" table, which appears leftmost in the JOIN clause are included. Unmatched rows in the right 
table do not appear.
• Right Outer Join: In Right Outer Join all rows in the second-named table i.e. "right" table, which appears rightmost in the JOIN clause are included. Unmatched rows in 
the left table are not included.
• Full Outer Join: In Full Outer Join all rows in all joined tables are included, whether they are matched or not.

• 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 has a hierarchal reporting structure whereby one member of 
staff reports to another. Self Join can be Outer Join or Inner Join.

3. 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.

4. 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.
 

5. 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. Stored Procedure sp_addlinkedserver, 
sp_addlinkedsrvlogin will be used add new Linked Server.

6. 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.

7. What is Cursor?

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

8. 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.

9. 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.

10. What is 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 thought of as views 
that take parameters and can be used in JOINs and other Rowset operations.

11. 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 controlled. Identity/GUID columns do not 
need to be indexed.

12. What is Index?

An index is a physical structure containing pointers to the data. Indices are created in an 
existing table to locate rows more quickly and efficiently. It is possible to create an index on 
one or more columns of a table, and each index is given a name. The users cannot see the 
indexes; they are just used to speed up queries. Effective indexes are one of the best ways 
to improve performance in a database application. A table scan happens when there is no 
index available to help a query. In a table scan SQL Server examines every row in the table 
to satisfy the query results. Table scans are sometimes unavoidable, but on large tables, 
scans have a terrific impact on performance.

13. What is Nested Trigger?

A trigger can also contain INSERT, UPDATE and DELETE logic within itself, so 
when the trigger is fired because of data modification it can also cause another data 
modification, thereby firing another trigger. A trigger that contains data modification logic 
within itself is called a nested trigger.

14. What is Normalization?

Database normalization is a data design and organization process applied to data structures 
based on rules that help building relational databases. In relational database design, the 
process of organizing data to minimize redundancy is called normalization. Normalization 
usually involves dividing a database into two or more tables and defining relationships 
between the tables. The objective is to isolate data so that additions, deletions, and 
modifications of a field can be made in just one table and then propagated through the rest 
of the database via the defined relationships.

15. What is RDBMS?

Relational Data Base Management Systems (RDBMS) are database management systems 
that maintain data records and indices in tables. Relationships may be created and 
maintained across and among the data and tables. In a relational database, relationships 
between data items are expressed by means of tables. Interdependencies among these 
tables are expressed by data values rather than by pointers. This allows a high degree of 
data independence. An RDBMS has the capability to recombine the data items from 
different files, providing powerful tools for data usage.

16. What is Stored Procedure?

A stored procedure is a named group of SQL statements that have been previously created 
and stored in the server database. Stored procedures accept input parameters so that a 
single procedure can be used over the network by several clients using different input data. 
And when the procedure is modified, all clients automatically get the new version. Stored 
procedures reduce network traffic and improve performance. Stored procedures can be 
used to help ensure the integrity of the database.

 
e.g. sp_helpdb, sp_renamedb, sp_depends etc.

17. 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 resultset. 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.

18. What is Trigger?

A trigger is a SQL procedure that initiates an action when an event (INSERT, DELETE or 
UPDATE) occurs. Triggers are stored in and managed by the DBMS. Triggers are used to 
maintain the referential integrity of data by changing the data in a systematic fashion. A 
trigger cannot be called or executed; DBMS automatically fires the trigger as a result of a 
data modification to the associated table. Triggers can be viewed as similar to stored 
procedures in that both consist of procedural logic that is stored at the database level. 
Stored procedures, however, are not event-drive and are not attached to a specific table as 
triggers are. Stored procedures are explicitly executed by invoking a CALL to the procedure 
while triggers are implicitly executed. In addition, triggers can also execute stored 
procedures.

19. What is User Defined Functions? What kind of User-Defined Functions can be created?

User-Defined Functions allow defining its own T-SQL functions that can accept 0 or more 
parameters and return a single scalar data value or a table data type.

Different Kinds of User-Defined Functions created are:

• 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 TSQL 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.

20. What is View?

A simple view can be thought of as a subset of a table. It can be used for retrieving data, as 
well as updating or deleting rows. Rows updated or deleted in the view are updated or 
deleted in the table the view was created with. It should also be noted that as data in the 
original table changes, so does data in the view, as views are the way to look at part of the 
original table. The results of using a view are not permanently stored in the database. The 
data accessed through a view is actually constructed using standard T-SQL select command 
and can come from one to many different base tables or even other views.