1.Default constraints:
Default constraints enable the SQL Server to write default value to a column when user doesn’t specify a value.
Unique constraints:
A unique constraint restricts a column or combination of columns from allowing duplicate values.
Primary key constraints:
Primary key constraints will allow a row to be uniquely identified. This will perform by primary key on the table.
Foreign key constraints:
Foreign keys constraints will ensure that the values that can be entered in a particular column exist in a specified table.
2.What are the tradeoffs with having indexes?
(a) Faster selects, slower updates. (b) Extra storage space to store
indexes. Updates are slower because in addition to updating the table
you have to update the index
3. What is SQL?
SQL stands for Structured Query Language , and it is used to
communicate with the Database. This is a standard language used to
perform tasks such as retrieval, updation, insertion and deletion of
data from a database.
Standard SQL Commands are Select.
4. What is a Database?
Database is nothing but an organized form of data for easy access,
storing, retrieval and managing of data. This is also known as
structured form of data which can be accessed in many ways.
Example: School Management Database, Bank Management Database.
5. What are tables and Fields?
A table is a set of data that are organized in a model with Columns
and Rows. Columns can be categorized as vertical, and Rows are
horizontal. A table has specified number of column called fields but can
have any number of rows which is called record.
6. What is a primary key?
A primary key is a combination of fields which uniquely specify a
row. This is a special kind of unique key, and it has implicit NOT NULL
constraint. It means, Primary key values cannot be NULL.
7. What is a unique key?
A Unique key constraint uniquely identified each record in the
database. This provides uniqueness for the column or set of columns.
A Primary key constraint has automatic unique constraint defined on it. But not, in the case of Unique Key.
There can be many unique constraint defined per table, but only one Primary key constraint defined per table.
8. What is a foreign key?
A foreign key is one table which can be related to the primary key of
another table. Relationship needs to be created between two tables by
referencing foreign key with the primary key of another table.
9. What is a join?
This is a keyword used to query data from more tables based on the
relationship between the fields of the tables. Keys play a major role
when JOINs are used.
10. What are the types of join and explain each?
There are various types of join which can be used to retrieve data and it depends on the relationship between tables.
Inner join.
Inner join return rows when there is at least one match of rows between the tables.
Right Join.
Right join return rows which are common between the tables and all
rows of Right hand side table. Simply, it returns all the rows from the
right hand side table even though there are no matches in the left hand
side table.
Left Join.
Left join return rows which are common between the tables and all
rows of Left hand side table. Simply, it returns all the rows from Left
hand side table even though there are no matches in the Right hand side
table.
Full Join.
Full join return rows when there are matching rows in any one of the
tables. This means, it returns all the rows from the left hand side
table and all the rows from the right hand side table.
11. What is normalization?
Normalization is the process of minimizing redundancy and dependency
by organizing fields and table of a database. The main aim of
Normalization is to add, delete or modify field that can be made in a
single table.
12. What is Denormalization.
DeNormalization is a technique used to access the data from higher to
lower normal forms of database. It is also process of introducing
redundancy into a table by incorporating data from the related tables.
13. What are all the different normalizations?
The normal forms can be divided into 5 forms, and they are explained below -.
First Normal Form (1NF):.
This should remove all the duplicate columns from the table. Creation
of tables for the related data and identification of unique columns.
Second Normal Form (2NF):.
Meeting all requirements of the first normal form. Placing the
subsets of data in separate tables and Creation of relationships between
the tables using primary keys.
Third Normal Form (3NF):.
This should meet all requirements of 2NF. Removing the columns which are not dependent on primary key constraints.
Fourth Normal Form (3NF):.
Meeting all the requirements of third normal form and it should not have multi- valued dependencies.
14. What is a View?
A view is a virtual table which consists of a subset of data
contained in a table. Views are not virtually present, and it takes less
space to store. View can have data of one or more tables combined, and
it is depending on the relationship.
15. What is an Index?
An index is performance tuning method of allowing faster retrieval of
records from the table. An index creates an entry for each value and it
will be faster to retrieve data.
16. What are all the different types of indexes?
There are three types of indexes -.
Unique Index.
This indexing does not allow the field to have duplicate values if
the column is unique indexed. Unique index can be applied automatically
when primary key is defined.
Clustered Index.
This type of index reorders the physical order of the table and
search based on the key values. Each table can have only one clustered
index.
NonClustered Index.
NonClustered Index does not alter the physical order of the table and
maintains logical order of data. Each table can have 999 nonclustered
indexes
.
17. What is a Cursor?
A database Cursor is a control which enables traversal over the rows
or records in the table. This can be viewed as a pointer to one row in a
set of rows. Cursor is very much useful for traversing such as
retrieval, addition and removal of database records.
18. What is a relationship and what are they?
Database Relationship is defined as the connection between the tables
in a database. There are various data basing relationships, and they
are as follows:.
- One to One Relationship.
- One to Many Relationship.
- Many to One Relationship.
- Self-Referencing Relationship.
19. What is a query?
A DB query is a code written in order to get the information back
from the database. Query can be designed in such a way that it matched
with our expectation of the result set. Simply, a question to the
Database.
20. What is subquery?
A subquery is a query within another query. The outer query is called
as main query, and inner query is called subquery. SubQuery is always
executed first, and the result of subquery is passed on to the main
query.
21. What are the types of subquery?
There are two types of subquery – Correlated and Non-Correlated.
A correlated subquery cannot be considered as independent query, but
it can refer the column in a table listed in the FROM the list of the
main query.
A Non-Correlated sub query can be considered as independent query and the output of subquery are substituted in the main query.
22. What is a stored procedure?
Stored Procedure is a function consists of many SQL statement to
access the database system. Several SQL statements are consolidated into
a stored procedure and execute them whenever and wherever required.
23. What is a trigger?
A DB trigger is a code or programs that automatically execute with
response to some event on a table or view in a database. Mainly, trigger
helps to maintain the integrity of the database.
Example: When a new student is added to the student database, new
records should be created in the related tables like Exam, Score and
Attendance tables.
24. What is the difference between DELETE and TRUNCATE commands?
DELETE command is used to remove rows from the table, and WHERE
clause can be used for conditional set of parameters. Commit and
Rollback can be performed after delete statement.
TRUNCATE removes all rows from the table. Truncate operation cannot be rolled back.
25. What are local and global variables and their differences?
Local variables are the variables which can be used or exist inside
the function. They are not known to the other functions and those
variables cannot be referred or used. Variables can be created whenever
that function is called.
Global variables are the variables which can be used or exist
throughout the program. Same variable declared in global cannot be used
in functions. Global variables cannot be created whenever that function
is called.
26. What is a constraint?
Constraint can be used to specify the limit on the data type of
table. Constraint can be specified while creating or altering the table
statement. Sample of constraint are.
- NOT NULL.
- CHECK.
- DEFAULT.
- UNIQUE.
- PRIMARY KEY.
- FOREIGN KEY.
27. What is data Integrity?
Data Integrity defines the accuracy and consistency of data stored in
a database. It can also define integrity constraints to enforce
business rules on the data when it is entered into the application or
database.
28. What is Auto Increment?
Auto increment keyword allows the user to create a unique number to
be generated when a new record is inserted into the table. AUTO
INCREMENT keyword can be used in Oracle and IDENTITY keyword can be used
in SQL SERVER.
Mostly this keyword can be used whenever PRIMARY KEY is used.
29. What is the difference between Cluster and Non-Cluster Index?
Clustered index is used for easy retrieval of data from the database
by altering the way that the records are stored. Database sorts out rows
by the column which is set to be clustered index.
A nonclustered index does not alter the way it was stored but creates
a complete separate object within the table. It point back to the
original table rows after searching.
30. What is Datawarehouse?
Datawarehouse is a central repository of data from multiple sources
of information. Those data are consolidated, transformed and made
available for the mining and online processing. Warehouse data have a
subset of data called Data Marts.
