Top 100 SQL Interview Questions and Answers

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TOP 100INTERVIEW QUESTIONS & ANSWERS

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What is DBMS?

2

QUESTION

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.

ANSWER

QUESTION 1

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What is RDBMS?

3

QUESTION

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.

ANSWER

QUESTION 2



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What is SQL?

4

QUESTION

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.

ANSWER

QUESTION 3



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What is a Database?

5

QUESTION

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.

ANSWER

QUESTION 4



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What are tables and Fields?

6

QUESTION

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.

ANSWER

QUESTION 5



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What is a primary key?

7

QUESTION

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.

ANSWER

QUESTION 6



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What is a unique key?

8

QUESTION

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.

ANSWER

QUESTION 7



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What is a foreign key?

9

QUESTION

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.

ANSWER

QUESTION 8



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What are the types of join and explain each?

10

QUESTION

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.

ANSWER

QUESTION 9



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Explain an outer join?

11

QUESTION

An outer join includes rows from tables when there are no matching values in the tables.

ANSWER

QUESTION 10



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What is normalization?

12

QUESTION

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.

ANSWER

QUESTION 11



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What is Denormalization?

13

QUESTION

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.

ANSWER

QUESTION 12



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What are all the different normalizations?

14

QUESTION

The normal forms can be divided into 4 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 (4NF): Meeting all the requirements of third normal form and it should not have multi-

valued dependencies.

ANSWER

QUESTION 13



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What is an Index? What are all the different types of indexes?

15

QUESTION

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.

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.

Non Clustered Index: Non Clustered Index does not alter the physical order of the table and maintains logical

order of data. Each table can have 999 non clustered indexes.

ANSWER

QUESTION 14



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What is a relationship and what are they?

16

QUESTION

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.

ANSWER

QUESTION 15



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What is a query?

17

QUESTION

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.

ANSWER

QUESTION 16



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What is subquery? What are the types of subquery?

18

QUESTION

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.

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.

ANSWER

QUESTION 17



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What is a trigger?

19

QUESTION

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.

ANSWER

QUESTION 18



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What are the types of Triggers?

20

QUESTION

There are four types of triggers and they are:

• Insert

• Delete

• Update

• Instead of

ANSWER

QUESTION 19



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What is the difference between DELETE TRUNCATE and DROP commands?

21

QUESTION

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.

Drop command is used to drop the table or keys like primary, foreign from a table.

ANSWER

QUESTION 20



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What is data Integrity?

22

QUESTION

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.

ANSWER

QUESTION 21



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What is collation?

23

QUESTION

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.

ANSWER

QUESTION 22



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Advantages and Disadvantages of Stored Procedure?

24

QUESTION

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.

ANSWER

QUESTION 23



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What is SQL Injection ?

25

QUESTION

SQL Injection is one of the techniques uses by hackers to hack a website by injecting SQL commands in data fields.

ANSWER

QUESTION 24



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What is the difference between a HAVING CLAUSE and a WHERE CLAUSE?

26

QUESTION

They specify a search condition for a group or an aggregate. But the difference is that 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 whereas WHERE Clause is applied to each row before they are part of the GROUP BY function in a query.

ANSWER

QUESTION 25



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How would apply date range filter?

27

QUESTION

a. You can use simple condition >= and <= or similar or use between/and but the trick is to know your exact data

type.

b. Sometimes date fields contain time and that is where the query can go wrong so it is recommended to use some

date related functions to remove the time issue. In SQL Server common function to do that is datediff function.

c. You also have to be aware of different time zones and server time zone.

d. To increase query performance you may still want to use between however you should be aware of proper format

you should use if not it might misbehave during filtering.

ANSWER

QUESTION 26



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What is the difference between JOIN and UNION?

28

QUESTION

SQL JOIN allows us to ―lookup‖ records on other table based on the given conditions between two tables. For

example, if we have the department ID of each employee, then we can use this department ID of the employee

table to join with the department ID of department table to lookup department names.

UNION operation allows us to add 2 similar data sets to create resulting data set that contains all the data from the

source data sets. Union does not require any condition for joining. For example, if you have 2 employee tables

with same structure, you can UNION them to create one result set that will contain all the employees from both of

the tables.

SELECT * FROM EMP1

UNION

SELECT * FROM EMP2;

ANSWER

QUESTION 27



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What is the difference among UNION, MINUS and INTERSECT?

29

QUESTION

UNION combines the results from 2 tables and eliminates duplicate records from the result set.

MINUS operator when used between 2 tables, gives us all the rows from the first table except the rows which are

present in the second table.

INTERSECT operator returns us only the matching or common rows between 2 result sets.

ANSWER

QUESTION 28



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What is Self Join and why is it required?

30

QUESTION

Self Join is the act of joining one table with itself. Self Join is often very useful to convert a hierarchical structure into

a flat structure

ANSWER

QUESTION 29



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How can we transpose a table using SQL (changing rows to column or vice-versa)?

31

QUESTION

The usual way to do it in SQL is to use CASE statement or DECODE statement.

ANSWER

QUESTION 30



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What are the differences among ROWNUM, RANK and DENSE_RANK?

32

QUESTION

ROW_NUMBER assigns contiguous, unique numbers from 1.. N to a result set.

RANK does not assign unique numbers—nor does it assign contiguous numbers. If two records tie for second

place, no record will be assigned the 3rd rank as no one came in third, according to RANK.

DENSE_RANK, like RANK, does not assign unique numbers, but it does assign contiguous numbers. Even though

two records tied for second place, there is a third-place record.

ANSWER

QUESTION 31



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What is a database transaction?

33

QUESTION

Database transaction take database from one consistent state to another. At the end of the transaction the system

must be in the prior state if transaction fails or the status of the system should reflect the successful completion if

the transaction goes through.

ANSWER

QUESTION 32



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What are properties of a transaction?

34

QUESTION

Properties of the transaction can be summarized as ACID Properties.

1. Atomicity: A transaction consists of many steps. When all the steps in a transaction gets completed, it will get

reflected in DB or if any step fails, all the transactions are rolled back.

2. Consistency: The database will move from one consistent state to another, if the transaction succeeds and

remain in the original state, if the transaction fails.

3. Isolation: Every transaction should operate as if it is the only transaction in the system

4. Durability: Once a transaction has completed successfully, the updated rows/records must be available for all

other transactions on a permanent basis

ANSWER

QUESTION 33



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What is a Database Lock? What are the type of locks?

35

QUESTION

Database lock tell a transaction, if the data item in questions is currently being used by other transactions.

1. Shared Lock: When a shared lock is applied on data item, other transactions can only read the item, but can't

write into it.

2. Exclusive Lock: When a exclusive lock is applied on data item, other transactions can't read or write into the data

item.

ANSWER

QUESTION 34



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What is a Composite Key?

36

QUESTION

A Composite primary key is a type of candidate key, which represents a set of columns whose values uniquely

identify every row in a table.

For example - if "Employee_ID" and "Employee Name" in a table is combined to uniquely identifies a row its called

a Composite Key.

ANSWER

QUESTION 35



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What is a Composite Primary Key?

37

QUESTION

A Composite primary key is a set of columns whose values uniquely identify every row in a table. What it means is

that, table which contains composite primary key will be indexed based on columns specified in the primary key.

This key will be referred in Foreign Key tables.

For example - if combined effect of columns, "Employee_ID" and "Employee Name" in a table is required to uniquely

identifies a row, its called a Composite Primary Key. In this case, both the columns will be represented as primary

key.

ANSWER

QUESTION 36



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Define SQL Insert Statement?

38

QUESTION

SQL INSERT statement is used to add rows to a table. For a full row insert, SQL Query should start with ―insert into

―statement followed by table name and values command, followed by the values that need to be inserted into the

table. Insert can be used in several ways:

1. To insert a single complete row

2. To insert a single partial row

ANSWER

QUESTION 37



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Define SQL Update Statement?

39

QUESTION

SQL Update is used to update data in a row or set of rows specified in the filter condition.

The basic format of an SQL UPDATE statement is ,Update command followed by table to be updated and SET

command followed by column names and their new values followed by filter condition that determines which rows

should be updated.

ANSWER

QUESTION 38



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What are wild cards used in database for Pattern Matching?

40

QUESTION

SQL Like operator is user for pattern matching. SQL 'Like' command takes more time to process. So before using

like operator, consider suggestions given below on when and where to use wild card search.

1) Don't overuse wild cards. If another search operator will do, use it instead.

2) When you do use wild cards, try not to use them at the beginning of the search pattern, unless absolutely

necessary. Search patterns that begin with wild cards are the slowest to process.

3) Pay careful attention to the placement of the wild card symbols. If they are misplaced, you might not return the

data you intended

ANSWER

QUESTION 39



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What is Cross Join?

41

QUESTION

Cross Join will return all records where each row from the first table is combined with each row from the second

table.

ANSWER

QUESTION 40



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What is a view?

42

QUESTION

Views are virtual tables. Unlike tables that contain data, views simply contain queries that dynamically retrieve data

when used.

ANSWER

QUESTION 41



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What is a materialized view?

43

QUESTION

Materialized views is also a view but are disk based. Materialized views get updated on specific duration, base upon

the interval specified in the query definition. We can index materialized view.

ANSWER

QUESTION 42



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What are the advantages and disadvantages of views in a database?

44

QUESTION

Advantages:

1. Views doesn't store data in a physical location.

2. View can be use to hide some of the columns from the table

3. Views can provide Access Restriction, since data insertion, update and deletion is not possible on the view.

Disadvantages:

1. When a table is dropped, associated view become irrelevant.

2. Since view are created when a query requesting data from view is triggered, its bit slow

3. When views are created for large tables, it occupy more memory.

ANSWER

QUESTION 43



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When do you use UPDATE_STATISTICS command?

45

QUESTION

This command is used when a large processing of data has occurred. If any large amount of deletions, any

modifications, 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.

ANSWER

QUESTION 44



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What is an IDENTITY column in insert statements?

46

QUESTION

IDENTITY column is used in table columns to make that column as Auto incremental number or a surrogate key.

ANSWER

QUESTION 45



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How will I retrieve all records of employment 1 those should not be present n

employment 2?

47

QUESTION

(Select * from employment 2)-(Select * from employment 1).

ANSWER

QUESTION 46



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Which TCP/IP port does SQL Server run on? How can it be changed?

48

QUESTION

SQL Server runs on port 1433. It can be changed from the Network Utility TCP/IP properties.

ANSWER

QUESTION 47



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What is SQL Server Agent?

49

QUESTION

SQL Server agent plays an important role in the day-to-day tasks of a database administrator (DBA). 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.

ANSWER

QUESTION 48



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Which command using Query Analyzer will give you the version of SQL server and

operating system?

50

QUESTION

SELECT SERVERPROPERTY ('productversion'), SERVERPROPERTY ('productlevel') and SERVERPROPERTY

('edition')

ANSWER

QUESTION 49



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How to create recursive query in SQL Server?

51

QUESTION

Recursive query can be create in SQL using stored procedure but you can also use CTE (Common table

expression). It might be also worth asking about performance as CTE is not always very fast.

ANSWER

QUESTION 51



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What is a constraint?

52

QUESTION

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.

ANSWER

QUESTION 51



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What is Auto Increment?

53

QUESTION

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.

ANSWER

QUESTION 52



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What is Datawarehouse?

54

QUESTION

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.

ANSWER

QUESTION 53



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What is user defined functions?

55

QUESTION

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.

ANSWER

QUESTION 54



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What are all types of user defined functions?

56

QUESTION

Three types of user defined functions are.

a. Scalar Functions.

b. Inline Table valued functions.

c. Multi statement valued functions.

ANSWER

QUESTION 55



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What are all different types of collation sensitivity?

57

QUESTION

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.

ANSWER

QUESTION 56



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What is Online Transaction Processing (OLTP)?

58

QUESTION

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.

ANSWER

QUESTION 57



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What is an ALIAS command?

59

QUESTION

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-.

Select st.StudentID, Ex.Result from student st, Exam as Ex where st.studentID = Ex. StudentID

Here, st refers to alias name for student table and Ex refers to alias name for exam table.

ANSWER

QUESTION 58



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What are aggregate and scalar functions?

60

QUESTION

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.

ANSWER

QUESTION 59



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How can you create an empty table from an existing table?

61

QUESTION

Select * into studentcopy from student where 1=2

Here, we are copying student table to another table with the same structure with no rows copied.

ANSWER

QUESTION 60



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How to fetch common records from two tables?

62

QUESTION

Common records result set can be achieved by -.

Select studentID from student. <strong>INTERSECT </strong> Select StudentID from Exam

ANSWER

QUESTION 61



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How to select unique records from a table?

63

QUESTION

Select unique records from a table by using DISTINCT keyword.

Select DISTINCT StudentID, StudentName from Student.

ANSWER

QUESTION 62



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What are the different index configurations a table can have?

64

QUESTION

A table can have one of the following index configurations:

1. No indexes

2. A clustered index

3. A clustered index and many nonclustered indexes

4. A nonclustered index

5. Many nonclustered indexes

ANSWER

QUESTION 63



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What are the properties and different Types of Sub-Queries?

65

QUESTION

Properties of Sub-Query

a. A sub-query must be enclosed in the parenthesis.

b. A sub-query must be put in the right hand of the comparison operator, and

c. A sub-query cannot contain an ORDER-BY clause.

d. A query can contain more than one sub-query.

Types of Sub-Query

e. Single-row sub-query, where the sub-query returns only one row.

f. Multiple-row sub-query, where the sub-query returns multiple rows,. and

g. Multiple column sub-query, where the sub-query returns multiple columns

ANSWER

QUESTION 64



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What is SQL Profiler?

66

QUESTION

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 performances

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.

ANSWER

QUESTION 65



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What are the authentication modes in SQL Server? How can it be changed?

67

QUESTION

Windows mode and Mixed Mode - SQL and 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.

ANSWER

QUESTION 66



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Can a stored procedure call itself or recursive stored procedure? How much level

SP nesting is possible?

68

QUESTION

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.

ANSWER

QUESTION 67



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What is Log Shipping?

69

QUESTION

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 and can be used this as the Disaster Recovery

plan. The key feature of log shipping is that it will automatically backup transaction logs throughout the day and

automatically restore them on the standby server at defined interval.

ANSWER

QUESTION 68



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Name 3 ways to get an accurate count of the number of records in a table?

70

QUESTION

SELECT * FROM table1

SELECT COUNT(*) FROM table1

SELECT rows FROM sysindexes WHERE id = OBJECT_ID(table1) AND indid < 2

ANSWER

QUESTION 69



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What does it mean to have QUOTED_IDENTIFIER ON? What are the implications of

having it OFF?

71

QUESTION

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.

ANSWER

QUESTION 70



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What is the difference between a Local and a Global temporary table?

72

QUESTION

1. 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.

2. A global temporary table remains in the database permanently, but the rows exist only within a given connection.

When connection is 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.

ANSWER

QUESTION 71



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How Global temporary tables are represented and its scope?

73

QUESTION

Global temporary tables are represented with ## before the table name. Scope will be the outside the session

whereas local temporary tables are inside the session. Session ID can be found using @@SPID.

ANSWER

QUESTION 72



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What is the STUFF function and how does it differ from the REPLACE function?

74

QUESTION

STUFF function is used 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 occurrences.

Using the 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.

ANSWER

QUESTION 73



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What is CHECK Constraint?

75

QUESTION

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.

ANSWER

QUESTION 74



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What is the difference between UNION and UNION ALL?

76

QUESTION

UNION statement is mainly used to combine the tables including the duplicate rows and UNION ALL combine but

does not look for duplicate rows. With this, UNION ALL will be very faster than UNION statements.

ANSWER

QUESTION 75



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What is NOT NULL Constraint?

77

QUESTION

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.

ANSWER

QUESTION 76



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How to get @@ERROR and @@ROWCOUNT at the same time?

78

QUESTION

If @@Rowcount is checked after Error checking statement then it will have 0 as the value of @@Recordcount as it

would have been reset. And if @@Recordcount is checked before the error-checking statement then @@Error

would get reset. To get @@error and @@rowcount at the same time do both in same statement and store them

in local variable.

SELECT @RC = @@ROWCOUNT, @ER = @@ERROR

ANSWER

QUESTION 77



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What is a Scheduled Jobs or What is a Scheduled Tasks?

79

QUESTION

Scheduled tasks let user automate processes that run on regular or predictable cycles. User can schedule

administrative tasks, such as cube processing, to run during times of slow business activity. User can also

determine the order in which tasks run by creating job steps within a SQL Server Agent job. E.g. back up

database, Update Stats of Tables. Job steps give user control over flow of execution. If one job fails, user can

configure SQL Server Agent to continue to run the remaining tasks or to stop execution.

ANSWER

QUESTION 78



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What is a table called, if it has neither Cluster nor Non-cluster Index? What is it

used for?

80

QUESTION

Unindexed table or Heap. Microsoft Press Books and Book on Line (BOL) refers it as Heap. A heap is a table that

does not have a clustered index and, therefore, the pages are not linked by pointers. The IAM pages are the only

structures that link the pages in a table together. Unindexed tables are good for fast storing of data. Many times it

is better to drop all indexes from table and then do bulk of inserts and to restore those indexes after that.

ANSWER

QUESTION 79



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Can SQL Servers linked to other servers like Oracle?

81

QUESTION

SQL Server can be linked to any server provided it has OLE-DB provider from Microsoft to allow a link. E.g. Oracle

has an OLE-DB provider for oracle that Microsoft provides to add it as linked server to SQL Server group.

ANSWER

QUESTION 80



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What is BCP? When does it used?

82

QUESTION

BulkCopy is a tool used to copy huge amount of data from tables and views. BCP does not copy the structures

same as source to destination. BULK INSERT command helps to import a data file into a database table or view

in a user-specified format.

ANSWER

QUESTION 81



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How to implement one-to-one, one-to-many and many-to-many relationships while

designing tables?

83

QUESTION

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.

ANSWER

QUESTION 82



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What is an execution plan? When would you use it? How would you view the

execution plan?

84

QUESTION

An execution plan is basically a road map that graphically or textually shows the data retrieval methods chosen by

the SQL Server query optimizer for a stored procedure or ad- hoc query and is a very useful tool for a developer

to understand the performance characteristics of a query or stored procedure since the plan is the one that SQL

Server will place in its cache and use to execute the stored procedure or query. From within Query Analyzer is an

option called "Show Execution Plan" (located on the Query drop-down menu). If this option is turned on it will

display query execution plan in separate window when query is ran again.

ANSWER

QUESTION 83



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What are the two authentication modes in SQL Server?

85

QUESTION

There are two authentication modes –

• Windows Mode

• Mixed Mode

Modes can be changed by selecting the tools menu of SQL Server configuration properties and choose security

page.

ANSWER

QUESTION 84



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What is COALESCE in SQL Server?

86

QUESTION

COALESCE is used to return first non-null expression within the arguments. This function is used to return a non-

null from more than one column in the arguments.

Example –

Select COALESCE(empno, empname, salary) from employee;

ANSWER

QUESTION 85



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How exceptions can be handled in SQL Server Programming?

87

QUESTION

Exceptions are handled using TRY—-CATCH constructs and it is handles by writing scripts inside the TRY block

and error handling in the CATCH block.

ANSWER

QUESTION 86



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What is the purpose of FLOOR function?

88

QUESTION

FLOOR function is used to round up a non-integer value to the previous least integer. Example is given FLOOR(6.7)

Returns 6.

ANSWER

QUESTION 87



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Can we check locks in database? If so, how can we do this lock check?

89

QUESTION

Yes, we can check locks in the database. It can be achieved by using in-built stored procedure called sp_lock.

ANSWER

QUESTION 88



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What is the use of SIGN function?

90

QUESTION

SIGN function is used to determine whether the number specified is Positive, Negative and Zero. This will return

+1,-1 or 0.

Example: SIGN(-35) returns -1

ANSWER

QUESTION 89



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How is the SUBSTR keyword used in SQL?

91

QUESTION

SUBSTR is used for string manipulation with column name, first position and string length used as arguments. E.g.

SUBSTR (NAME, 1 3) refers to the first three characters in the column NAME.

ANSWER

QUESTION 90



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What is a NULL value? What are the pros and cons of using NULLS?

92

QUESTION

A NULL value takes up one byte of storage and indicates that a value is not present as opposed to a space or zero

value. It's the DB2 equivalent of TBD on an organizational chart and often correctly portrays a business situation.

Unfortunately, it requires extra coding for an application program to handle this situation.

ANSWER

QUESTION 91



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What is a synonym? How is it used?

93

QUESTION

A synonym is used to reference a table or view by another name. The other name can then be written in the

application code pointing to test tables in the development stage and to production entities when the code is

migrated. The synonym is linked to the AUTHID that created it.

ANSWER

QUESTION 92



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What is a Cartesian product?

94

QUESTION

A Cartesian product results from a faulty query. It is a row in the results for every combination in the join tables.

ANSWER

QUESTION 93



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What is a tuple?

95

QUESTION

Static SQL is compiled and optimized prior to its execution; dynamic is compiled and optimized during execution.

ANSWER

QUESTION 94



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What is referential integrity?

96

QUESTION

Referential integrity refers to the consistency that must be maintained between primary and foreign keys, i.e. every

foreign key value must have a corresponding primary key value.

ANSWER

QUESTION 95



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What’s the maximum size of a row?

97

QUESTION

8060 bytes.

ANSWER

QUESTION 96



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How to change Database name in SQL server?

98

QUESTION

Use the following code:

Supported in SQL server 2000 and 2005

Exec sp_renamedb ―test‖, ―test1‖

Supported in SQL Server 2005 and later version

ALTER Database ―test1‖ Modify Name = ―test‖

ANSWER

QUESTION 97



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What is a Cursor?

99

QUESTION

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.

ANSWER

QUESTION 98



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What are Magic Tables in SQL Server?

100

QUESTION

Insert and Delete tables are created when the trigger is fired for any DML command. Those tables are called Magic

Tables in SQL Server. These magic tables are used inside the triggers for data transaction.

ANSWER

QUESTION 99



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What is ISNULL() operator?

101

QUESTION

ISNULL function is used to check whether value given is NULL or not NULL in sql server. This function also provides

to replace a value with the NULL.

ANSWER

QUESTION 100



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Resources

102

http://www.itechaleart.com/2013/05/top-50-sql-question-answers_11.htmlhttps://www.katieandemil.com/sql-interview-questions-and-answers?tab=article#Question 4http://www.dwbiconcepts.com/tutorial/24-interview-questions/190-top-20-sql-interview-questions-with-answers.htmlhttp://a4academics.com/interview-questions/53-database-and-sql/411-sql-interview-questions-and-answers-databasehttp://narendra86.blogspot.com/2013/10/top-80-sql-query-interview-questions.htmlhttp://crackaninterview.com/sql-queries-interview-questions-answers/http://career.guru99.com/top-50-sql-question-answers/http://www.indiabix.com/technical/sql-server-common-questions/http://career.guru99.com/top-50-sql-server-questions-answers/http://www.ittestpapers.com/sql-interview-questions(25-50).htmlhttp://www.dotnetfunda.com/interviews/cat/8/sql-serverhttp://www.careerride.com/SQLServer-Interview-Questions.aspx


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Top 100 SQL Interview Questions and Answers