SQL SERVER CONCEPT INTERVIEW QUESTIONS AND ANSWERS WITH EXAMPLE .
1. What is
DBMS?
A Database Management System (DBMS) is a program
that controls creation, maintenance and use of a database. DBMS can be termed
as File Manager that manages data in a database rather than saving it in file
systems.
2. What is
RDBMS?
RDBMS stands for Relational Database Management
System. RDBMS store the data into the collection of tables, which is related by
common fields between the columns of the table. It also provides relational
operators to manipulate the data stored into the tables.
Example: SQL Server.
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.
Example:.
Table: Employee.
Field: Emp ID, Emp Name, Date of Birth.
Data: 201456, David, 11/15/1960.
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.
31. What is Self-Join?
Self-join is set to be query used to compare to
itself. This is used to compare values in a column with other values in the
same column in the same table. ALIAS ES can be used for the same table
comparison.
32. What is Cross-Join?
Cross join defines as Cartesian product where number
of rows in the first table multiplied by number of rows in the second table. If
suppose, WHERE clause is used in cross join then the query will work like an
INNER JOIN.
33. What is user defined
functions?
User defined functions are the functions written to
use that logic whenever required. It is not necessary to write the same logic
several times. Instead, function can be called or executed whenever needed.
34. What are all types of
user defined functions?
Three types of user defined functions are.
§ Scalar Functions.
§ Inline Table valued functions.
§ Multi statement valued functions.
Scalar returns unit, variant defined the return
clause. Other two types return table as a return.
35. What is collation?
Collation is defined as set of rules that determine
how character data can be sorted and compared. This can be used to compare A
and, other language characters and also depends on the width of the characters.
ASCII value can be used to compare these character
data.
36. What are all different types
of collation sensitivity?
Following are different types of collation
sensitivity -.
§ Case Sensitivity – A and a and B and b.
§ Accent Sensitivity.
§ Kana Sensitivity – Japanese Kana characters.
§ Width Sensitivity – Single byte character and
double byte character.
37. Advantages and Disadvantages
of Stored Procedure?
Stored procedure can be used as a modular
programming – means create once, store and call for several times whenever
required. This supports faster execution instead of executing multiple queries.
This reduces network traffic and provides better security to the data.
Disadvantage is that it can be executed only in the
Database and utilizes more memory in the database server.
38. What is Online Transaction
Processing (OLTP)?
Online Transaction Processing or OLTP manages
transaction based applications which can be used for data entry and easy
retrieval processing of data. This processing makes like easier on simplicity
and efficiency. It is faster, more accurate results and expenses with respect
to OTLP.
Example – Bank Transactions on a daily basis.
39. What is CLAUSE?
SQL clause is defined to limit the result set by
providing condition to the query. This usually filters some rows from the whole
set of records.
Example – Query that has WHERE condition
Query that has HAVING condition.
40. What is recursive stored
procedure?
A stored procedure which calls by itself until it
reaches some boundary condition. This recursive function or procedure helps
programmers to use the same set of code any number of times.
41. What is Union, minus and
Interact commands?
UNION operator is used to combine the results of
two tables, and it eliminates duplicate rows from the tables.
MINUS operator is used to return rows from the
first query but not from the second query. Matching records of first and second
query and other rows from the first query will be displayed as a result set.
INTERSECT operator is used to return rows returned
by both the queries.
42. What is an ALIAS
command?
ALIAS name can be given to a table or column. This
alias name can be referred in WHERE clause to identify the table or column.
Example-.
[sql]
Select st.StudentID, Ex.Result from student st, Exam as Ex where st.studentID = Ex. StudentID
[/sql]
Select st.StudentID, Ex.Result from student st, Exam as Ex where st.studentID = Ex. StudentID
[/sql]
Here, st refers to alias name for student table and
Ex refers to alias name for exam table.
43. What is the difference between
TRUNCATE and DROP statements?
TRUNCATE removes all the rows from the table, and
it cannot be rolled back. DROP command removes a table from the database and
operation cannot be rolled back.
44. What are aggregate and scalar
functions?
Aggregate functions are used to evaluate
mathematical calculation and return single values. This can be calculated from
the columns in a table. Scalar functions return a single value based on the
input value.
Example -.
Aggregate – max(), count – Calculated with respect
to numeric.
Scalar – UCASE(), NOW() – Calculated with respect
to strings.
45. How can you create an empty
table from an existing table?
Example will be -.
[sql]
Select * into studentcopy from student where 1=2.[/sql]
Select * into studentcopy from student where 1=2.[/sql]
Here, we are copying student table to another table
with the same structure with no rows copied.
46. How to fetch common
records from two tables?
Common records result set can be achieved by -.
[sql]Select studentID from student.
<strong>INTERSECT </strong>
Select StudentID from Exam.[/sql]
47. How to fetch alternate records
from a table?
Records can be fetched for both Odd and Even row
numbers -.
To display even numbers-.
[sql]Select studentId from (Select rowno, studentId
from student) where mod(rowno,2)=0.[/sql]
To display odd numbers-.
[sql]Select studentId from (Select rowno, studentId
from student) where mod(rowno,2)=1.[/sql]
48. How to select
unique records from a table?
Select unique records from a table by using
DISTINCT keyword.
[sql]
Select DISTINCT StudentID, StudentName from
Student.
[/sql]
49. What is the command used to
fetch first 5 characters of the string?
There are many ways to fetch first 5 characters of
the string -.
[sql]Select SUBSTRING(StudentName,1,5) as
studentname from student.[/sql]
[sql]Select RIGHT(Studentname,5) as studentname
from student.[/sql]
50. Which operator is used in
query for pattern matching?
LIKE operator is used for pattern matching, and it
can be used as -.
1.
%
– Matches zero or more characters.
2.
_(Underscore)
– Matching exactly one character.
Example -.
[sql]Select * from Student where studentname like
‘a%’[/sql]
[sql]Select * from Student where studentname like
‘ami_’[/sql]
Question: What
is the difference between where and having clause?
Answer: in SQL Where filters data on lowest row level. Having filters data after group by has been performed so it filters on "groups"
Answer: in SQL Where filters data on lowest row level. Having filters data after group by has been performed so it filters on "groups"
select
DATEADD(dd,-DAY(getdate())+1, getdate()) -- First day of current month
select
DATEADD(dd,-DAY(getdate()),DATEADD(mm, 1,getdate())) -- Last day of current
month
select
DATEADD(dd,-DAY(getdate())+1,DATEADD(mm,-1,getdate())) -- First day of previous month
select dateadd(mm,-1,DATEADD(dd,-DAY(getdate()),DATEADD(mm,1,getdate()))) -- Last day of previous month
SELECT
DATENAME(DAYOFYEAR, GETDATE()) as CurrentMonthName
select DATENAME(day,getdate())
--Using today's date
Select
CONVERT(nvarchar(8), getdate(),112) as [Date in YYYYMMDD Format]
select CONVERT(nvarchar(7),getdate(),112)
In
this tutorial I will show you how to return curent time in t-sql without date . Below are two
examples how you can do that.
Select cast(GetDate() as time) AS CurrentTime
The easiest
way to return Day Of Week using T-SQL is to use DATEPART function: Below is
example
SELECT DATEPART(D,GetDate())
"Microsoft called SQL Server's
implementation of the SQL as Transact-SQL (T-SQL)."
Just a nit-pick. Microsoft "calls" (uses) it that. It was Sybase that "called" (named) it that.
Just a nit-pick. Microsoft "calls" (uses) it that. It was Sybase that "called" (named) it that.
SQL is the
Structured Query Language, the ANSI/ISO Standard database language. SQL
Server's implementation of the language is called Transact-SQL (T-SQL).
select MAX(Salary) from Employee WHERE Salary NOT IN (select MAX(Salary) from Employee );
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SQL Statement
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Syntax
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AND / OR
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SELECT column_name(s)
FROM table_name WHERE condition AND|OR condition |
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ALTER TABLE
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ALTER TABLE table_name
ADD column_name datatype
or
ALTER TABLE table_name
DROP COLUMN column_name |
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AS (alias)
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SELECT column_name AS column_alias
FROM table_name
or
SELECT column_name
FROM table_name AS table_alias |
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BETWEEN
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SELECT column_name(s)
FROM table_name WHERE column_name BETWEEN value1 AND value2 |
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CREATE DATABASE
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CREATE DATABASE database_name
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CREATE TABLE
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CREATE TABLE table_name
( column_name1 data_type, column_name2 data_type, column_name2 data_type, ... ) |
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CREATE INDEX
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CREATE INDEX index_name
ON table_name (column_name)
or
CREATE UNIQUE INDEX
index_name
ON table_name (column_name) |
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CREATE VIEW
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CREATE VIEW view_name AS
SELECT column_name(s) FROM table_name WHERE condition |
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DELETE
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DELETE FROM table_name
WHERE some_column=some_value
or
DELETE FROM
table_name
(Note: Deletes the entire table!!)
DELETE * FROM
table_name
(Note: Deletes the entire table!!) |
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DROP DATABASE
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DROP DATABASE database_name
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DROP INDEX
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DROP INDEX table_name.index_name (SQL
Server)
DROP INDEX index_name ON table_name (MS Access) DROP INDEX index_name (DB2/Oracle) ALTER TABLE table_name DROP INDEX index_name (MySQL) |
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DROP TABLE
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DROP TABLE table_name
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GROUP BY
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SELECT column_name,
aggregate_function(column_name)
FROM table_name WHERE column_name operator value GROUP BY column_name |
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HAVING
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SELECT column_name, aggregate_function(column_name)
FROM table_name WHERE column_name operator value GROUP BY column_name HAVING aggregate_function(column_name) operator value |
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IN
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SELECT column_name(s)
FROM table_name WHERE column_name IN (value1,value2,..) |
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INSERT INTO
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INSERT INTO table_name
VALUES (value1, value2, value3,....)
or
INSERT INTO
table_name
(column1, column2, column3,...) VALUES (value1, value2, value3,....) |
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INNER JOIN
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SELECT column_name(s)
FROM table_name1 INNER JOIN table_name2 ON table_name1.column_name=table_name2.column_name |
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LEFT JOIN
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SELECT column_name(s)
FROM table_name1 LEFT JOIN table_name2 ON table_name1.column_name=table_name2.column_name |
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RIGHT JOIN
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SELECT column_name(s)
FROM table_name1 RIGHT JOIN table_name2 ON table_name1.column_name=table_name2.column_name |
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FULL JOIN
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SELECT column_name(s)
FROM table_name1 FULL JOIN table_name2 ON table_name1.column_name=table_name2.column_name |
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LIKE
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SELECT column_name(s)
FROM table_name WHERE column_name LIKE pattern |
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ORDER BY
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SELECT column_name(s)
FROM table_name ORDER BY column_name [ASC|DESC] |
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SELECT
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SELECT column_name(s)
FROM table_name |
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SELECT *
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SELECT *
FROM table_name |
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SELECT DISTINCT
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SELECT DISTINCT column_name(s)
FROM table_name |
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SELECT INTO
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SELECT *
INTO new_table_name [IN externaldatabase] FROM old_table_name
or
SELECT
column_name(s)
INTO new_table_name [IN externaldatabase] FROM old_table_name |
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SELECT TOP
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SELECT TOP number|percent
column_name(s)
FROM table_name |
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TRUNCATE TABLE
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TRUNCATE TABLE table_name
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UNION
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SELECT column_name(s) FROM
table_name1
UNION SELECT column_name(s) FROM table_name2 |
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UNION ALL
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SELECT column_name(s) FROM
table_name1
UNION ALL SELECT column_name(s) FROM table_name2 |
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UPDATE
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UPDATE table_name
SET column1=value, column2=value,... WHERE some_column=some_value |
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WHERE
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SELECT column_name(s)
FROM table_name WHERE column_name operator value |
Referential
integrity is a property of data which, when satisfied,
requires every value of one attribute (column) of a relation (table) to exist as a value of another attribute
in a different (or the same) relation (table).[1]
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