Database Testing Interview Questions By H2kInfosys

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Database Testing Interview Questions
Q. 1: What we normally check for in the Database Testing?
In Database Testing we need to check,
1) The field size validation
2) Check constraints.
3) Indexes are done or not (for performance related issues)
4) Stored procedures
5) The field size defined in the application is matching with that in the db.
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Q. 2: How can we do manual testing of database? Explain with an example
It involves observing operations that are operated on front-end are effected on the back-end or
not. The approach can be explained like:
While adding a record through the front-end, check back-end that addition of record is effected or
not. It applies to delete, update,......etc.
For Example: Enter the employee record in database through the front-end and check manually if
the record is added or not to the back-end.
=========================================================================
Q. 3: While doing database testing, how do we know that a trigger is fired or not?
It can be verified by querying the common audit log where we are able to see if the triggers is fired
or not.
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Q. 4: Is "A fast database retrieval rate" a testable requirement?
No. Since the requirement seems to be ambiguous. The SRS should clearly mention the
performance or transaction requirements i.e. It should specify clearly like - Database retrieval rate
of 5 microseconds.
==============================================================================
Q.5: What steps does a tester take in testing Stored Procedures?
First the tester should to go through the requirement, as to why the particular stored procedure is
written for.

Then check whether all the required indexes, joins, updates, deletions are correct comparing with
the tables mentioned in the Stored Procedure. And also he has to ensure whether the Stored
Procedure follows the standard format like comments, updated by, etc.
Then check the procedure calling name, calling parameters, and expected Reponses for different
sets of input parameters.
Then run the procedure yourself with database client programs like TOAD, or mysql, or Query
Analyzer
Rerun the procedure with different parameters, and check results against expected values.
Finally, automate the tests with QTP.
============================================================================
Q. 6: What SQL statements have you used in Database Testing?
-Both DDL and DML
===========================================================================
Q. 7: What are the test scenarios to test a database migrated from SQL Server 2005 to SQL Server
2008?
We need to check out what was all the enhancement the SQL Server 2008 has in it. We need to
design our test case considering the following points.
1) Data type used
2) Length of the data field it should be same as it was in SQL 2005
3) All the jobs should be scheduled properly
===========================================================================
Q. 8: What is primary key? Difference between Primary key and unique key
-Primary Key:
Can be only one in a table
It never allows null values
Primary Key is unique key identifier and can not be null and must be unique.
-Unique Key:
Can be more than one unique key in one table.
Unique key can have null values
It can’t be candidate key

Unique key can be null and may not be unique.
Q. 9: What are constrains?
-NULL,primary key,unique key,foriegn key,check,default
===============================================================================
Q. 10: Difference between DELETE, TRUNCATE AND DROP commands
TRUNCATE is a DDL command whereas DELETE is a DML command.
Hence DELETE operation can be rolled back, but TRUNCATE operation cannot be rolled
Drop can only be used to delete the whole table
==============================================================================
Q. 11: What is a stored procedure?
-SET of SQL statements
==============================================================================
Q. 12.What does the following query do:
SELECT SAL+NVL(COMMN,0) FROM EMP
-This displays the total salary of all employees. The null values in the commission column will be
replaced by 0 and added to salary.
==============================================================================
Q. 13.What is join? Explain different types of joins?
Join is a query, which retrieves related columns or rows from multiple tables.
Self Join - Joining the table with itself.
Equi Join - Joining two tables by equating two common columns.
Non-Equi Join - Joining two tables by equating two common columns.
Outer Join - Joining two tables in such a way that query can also retrieve rows that do not have
corresponding join value in the other table.
===========================================================================
Q. 14.Difference between stored procedures and a function
1> Procedure can return zero or n values whereas function can return one value which is
mandatory.

2>Procedures can have input,output parameters for it whereas functions can have only
input parameters.
3>Procedure allow select as well as DML statement in it whereas function allow only select
statement in it.
4>Functions can be called from procedure whereas procedures cannot be called from
function.
5.functions can be used in select statement procedures cannot .
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Q. 15. Describe how NULL works with SQL?
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Q. 16 can a table have more than one foreign key defined
-yes a table can more than one foreign key defined
================================================================================
Q. 17 which operator does you use to return all of the rows from one query except rows are
returned in a second query?
================================================================================
Q. 18.Describe some group functions you know
-These functions are: COUNT, MAX, MIN, AVG, SUM, DISTINCT
================================================================================
Q. 19. How will you update any column in a table
UPDATE table_name SET column_name = new_value WHERE column_name = some_value
================================================================================
Q. 20.Difference between UNION AND JOINS
- UNION - returns all distinct rows selected by either query
-jOINS retrieves related columns or rows from multiple tables.
================================================================================
Q. 21.how do you add record to a table
INSERT INTO table_name VALUES (value1, value2,....)
INSERT INTO table_name (column1, column2,...) VALUES (value1, value2,....)
===============================================================================

Q 22. What's Date Functions
Date Functions are ADD_MONTHS, LAST_DAY, NEXT_DAY, MONTHS_BETWEEN & SYSDATE.
==============================================================================
Q 23. What's Intersect
Intersect is the product of two tables listing only the matching rows.
===============================================================================
Q 24. Order of SQL statement execution
Where clause, Group By clause, having clause, Order By clause & Select.
===============================================================================
Q 25. Operators used in SELECT statements.
= Equal
<> or != Not equal
> Greater than
< Less than
>= Greater than or equal
<= Less than or equal
Between an inclusive range
LIKE Search for a pattern
===============================================================================
Q 26.How can you use Delete Statement:
DELETE FROM table_name WHERE column_name = some_value
Delete All Rows:
DELETE FROM table_name or DELETE * FROM table_name
==============================================================================
Q .27.Why does the following command give a compilation error?
DROP TABLE &TABLE_NAME; Variable names should start with an alphabet. Here the table name
starts with an '&' symbol.
==============================================================================

Q 28. State true or false. !=, <>, ^= all denote the same operation?
True.
==============================================================================
Q 29. 17. State true or false. EXISTS, SOME, ANY are operators in SQL?
True.
=============================================================================
Q.30. What is the value of comm and sal after executing the following query if the initial value of
‘sal’ is 10000
UPDATE EMP SET SAL = SAL + 1000, COMM = SAL*0.1;?
sal = 11000, comm = 1000.
=============================================================================
Q.31. What operator performs pattern matching?
LIKE operator.
============================================================================
Q 32. What operator tests column for the absence of data?
IS NULL operator.
============================================================================
Q 33.TRUNCATE TABLE EMP;
DELETE FROM EMP;
Will the outputs of the above two commands differ?
Both will result in deleting all the rows in the table EMP..
===========================================================================
Q34. What are the wildcards used for pattern matching?
_ for single character substitution and % for multi-character substitution.
===========================================================================
Q 35.Write SQL SELECT query that returns the first and last name of each instructor, the Salary,
and gives each of them a number.
A. SELECT FirstName, LastName, Salary, ROWNUM FROM Instructors;
=========================================================================

Q 36.Is the WHERE clause must appear always before the GROUP BY clause in SQL SELECT ?
A. Yes. The proper order for SQL SELECT clauses is: SELECT, FROM, WHERE, GROUP BY,
HAVING, ORDER BY. Only the SELECT and FROM clause are mandatory.
==========================================================================
Q.37.Write a query to return top N rows
Select Top 10 From tbl_name
============================================================================
Q 38.Select last N rows from the table
Select Top 10 From tbl_name Order by PK DESC
============================================================================
Q 39.Describe some Group Functions that you know
A. 1) The COUNT function tells you how many rows were in the result set.
SELECT COUNT(*) FROM TESTING.QA
2) The AVG function tells you the average value of a numeric column.
SELECT MAX(SALARY) FROM TESTING.QA
3) The MAX and MIN functions tell you the maximum and minimum value of a numeric column.
SELECT MIN(SALARY) FROM TESTING.QA
4) The SUM function tells you the sum value of a numeric column.
SELECT SUM(SALARY) FROM TESTING.QA
===========================================================================
40. How to get the count of employees with unique name from employee table:
SELECT COUNT (DISTINCT name) FROM employee;
============================================================================
41. While testing stored procedures what are the steps does a tester takes?
The tester will check the standard format of the stored procedures and also it checks the fields
are correct like updates, joins, indexes, deletions as mentioned in the stored procedure.
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Database Testing Interview Questions By H2kInfosys

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