• GUI Testing is AKA User Interface Testing or Front end testing
  Database Testing is AKA back-end testing or data testing.
• GUI Testing deals with all the testable items that are open to the user to interaction such as Menus, Forms etc.
  Database Testing deals with all the testable items that are generally hidden from the user.
• The tester who is performing GUI Testing doesn’t need to know Structured Query Language
  The tester who is performing Database Testing needs to know Structured Query Language
• GUI Testing includes in validating the text boxes, check boxes, buttons, drop-downs, forms etc., majorly the look and feel of the overall application
  Database Testing involves in verifying the integrity of data in the front end with the data present in the back end. It validates the schema, database tables, columns, indexes, stored procedures, triggers, data duplication, orphan records, junk records. It involves in updating records in database and verifying the same in the front end.

• DDL – Data Definition Language
• DML – Data Manipulation Language
• DQL – Data Query Language
• DCL – Data Control Language
• TCL – Transaction Control Language

• CREATE: To create databases and database objects
• ALTER: To alter existing database objects
• DROP: To drop databases and databases objects
• TRUNCATE: To remove all records from a table but not its database structure
• RENAME: To rename database objects

• COMMIT: To write and store the changes to the database
• ROLLBACK: To restore the database since a last commit

17. What is an Index?

CREATE VIEW view_name AS SELECT column_name1, column_name2 FROM table_name WHERE CONDITION;
           

 SELECT DISTINCT Name from tblEmployee
              

• INNER JOIN
• LEFT JOIN
• RIGHT JOIN
• OUTER JOIN

36. What is a NULL value?
A field with a NULL value is a field with no value. A NULL value is different from a zero value or a field that contains spaces. A field with a NULL value is one that has been left blank during record creation. Assume, there is a field in a table is optional and it is possible to insert a record without adding a value to the optional field then the field will be saved with a NULL value.

37. How to Test for NULL Values?
A field with a NULL value is a field with no value. NULL value cannot be compared with another NULL values. Hence, It is not possible to test for NULL values with comparison operators, such as =, <, or <>. For this, we have to use the IS NULL and IS NOT NULL operators.

SELECT column_names FROM table_name WHERE column_name IS NULL;

SELECT column_names FROM table_name WHERE column_name IS NOT NULL;

38. What is a NOT NULL constraint?
NOT NULL constraint is used to ensure that the value in the filed cannot be a NULL

39. What is a CHECK constraint?
CHECK constraint is used to limit the value that are accepted by one or more columns.

E.g. ‘Age’ field should contains only the value greater than 18.

CREATE TABLE EMP_DETAILS(EmpID int NOT NULL, NAME VARCHAR (30) NOT NULL, Age INT CHECK (AGE > 18), PRIMARY KEY (EmpID));

40. What is a DEFAULT constraint?
DEFAULT constraint is used to include a default value in a column when no value is supplied at the time of inserting a record.

44. Explain SQL Data Types?
In SQL Server, each column in a database table has a name and a data type. We need to decide what type of data to store inside each and every column of a table while creating a SQL table.

SELECT * INTO newtable FROM oldtable WHERE condition;

54. What is the difference between Union and Union All command?
This is one of the most important SQL Interview Questions
Union: It omits duplicate records and returns only distinct result set of two or more select statements.
Union All: It returns all the rows including duplicates in the result set of different select statements.

56. What are aggregate functions in SQL?
SQL aggregate functions return a single value, calculated from values in a column. Some of the aggregate functions in SQL are as follows

• AVG() – This functions returns the average value
• COUNT() – This functions returns the number of rows
• MAX() – This functions returns the largest value
• MIN() – This functions returns the smallest value
• ROUND() – This functions rounds a numeric field to the number of decimals specified
• SUM() – This functions returns the sum

57. What are string functions in SQL?
SQL string functions are used primarily for string manipulation. Some of the widely used SQL string functions are

• LEN() – It returns the length of the value in a text field
• LOWER() – It converts character data to lower case
• UPPER() – It converts character data to upper case
• SUBSTRING() – It extracts characters from a text field
• LTRIM() – It is to remove all white space from the beginning of the string
• RTRIM() – It is to remove all white space at the end of the string
• CONCAT() – Concatenate function combines multiple character strings together
• REPLACE() –  To update the content of a string.

Practical SQL Interview Questions:

58. How to add a new Employee details in an Employee_Details table with the following details

Employee_Name: John, Salary: 5500, Age: 29?

INSERT into Employee_Details (Employee_Name, Salary, Age) VALUES (‘John’, 5500 , 29);

59. How to add a column ‘Salary’ to a table Employee_Details?

ALTER TABLE Employee_Details ADD (Salary);

60. How to change value of the field ‘Salary’ as 7500 for an Employee_Name ‘John’ in a table Employee_Details?

UPDATE Employee_Details set Salary = 7500 where Employee_Name = ‘Sonam Thakur’;

61. How to select all records from the table?

Select * from table_name;

62. How To Get List of All Tables From A DataBase?
To view the tables available on a particular DataBase

USE TestDB
GO
SELECT * FROM sys.Tables
GO

63. Define SQL Delete statement.
The SQL Delete statement is used to delete records from a table.

DELETE FROM table_name WHERE some_column=some_value;

64. Write the command to remove all Players named Sachin from the Players table.

DELETE from Players WHERE Player_Name = ‘Santosh’

65. How to fetch values from TestTable1 that are not in TestTable2 without using NOT keyword?

--------------
| TestTable1 |
--------------
|     11     |
|     12     |
|     13     |
|     14     |
--------------

--------------
| TestTable2 |
--------------
|     11     |
|     12     |
--------------

By using the except keyword

SELECT * FROM TestTable1 EXCEPT SELECT * FROM TestTable2;

66. How to get each name only once from a employee table?
By using DISTINCT keyword, we could get each name only once.

SELECT DISTINCT employee_name FROM employee_table;

67. How to rename a column in the output of SQL query?
By using SQL AS keyword

SELECT column_name AS new_name FROM table_name;

68. What is the order of SQL SELECT ?
Order of SQL SELECT statement is as follows

SELECT, FROM, WHERE, GROUP BY, HAVING, ORDER BY.

69. How to display the current date in SQL.
By using below query

SELECT GetDate();

70. Write an SQL Query to find an Employee_Name whose Salary is equal or greater than 5000 from the below table Employee_Details.

|  Employee_Name   |  Salary|
-----------------------------
|  John            |  2500  |
|  Emma            |  3500  |
|  Mark            |  5500  |
|  Anne            |  6500  |
-----------------------------

Syntax:

SELECT Employee_Name FROM Employee_Details WHERE Salary>=5000;

Output:

|  Employee_Name   |  Salary|
-----------------------------
|  Mark            |  5500  |
|  Anne            |  6500  |
-----------------------------

|  Employee_Name   |  Salary|
-----------------------------
|  John            |  2500  |
|  Emma            |  3500  |
|  Mark            |  5500  |
|  Anne            |  6500  |
-----------------------------

SELECT * FROM Employee_Details WHERE Employee_Name like 'E%';

|  Employee_Name   |  Salary|
-----------------------------
|  Emma            |  3500  |
-----------------------------

SELECT FirstName, LastName FROM Employee_Details;

SP_RENAME TABLE 'SCOREBOARD', 'OVERALLSCORE'

sp_rename OldTableName,NewTableName
sp_rename 'TableName.OldColumnName', 'NewColumnName'

Select * from table where id % 2 = 0 

Select * from table where id % 2 != 0

SQL Case statement allows to embed an if-else like clause in the SELECT statement.

77. Can you display the result from the below table TestTable based on the criteria M,m as M and F, f as F and Null as N and g,k,I as U

SELECT Gender from TestTable

|  Gender  |
------------
|     M    |
|     F    |
|   NULL   |
|     m    |
|     f    | 
|     g    | 
|     H    | 
|     i    | 
------------

By using the below syntax we could achieve the output as required.

SELECT Gender,
case 
when Gender='i' then 'U' 
when Gender='g' then 'U'
when Gender='H' then 'U'
when Gender='NULL' then 'N'
else upper(Gender)
end as newgender from TestTable GROUP BY Gender

78. What will be the result of the query below? 

select case when null = null then 'SQLServer' else 'MySQL' end as Result;

This query will returns “MySQL”. In the above question we could see null = null is no the proper way to compare a null value.

79. What will be the result of the query below? 

select case when null is null then 'SQLServer' else 'MySQL' end as Result;

This query will returns “SQLServer”.

80. Can you display F as M and M as F from the below table TestTable. 

|  Name    |  Gender  |
------------------------
|  John    |     M    |
|  Emma    |     F    |
|  Mark    |     M    |
|  Anne    |     F    |
------------------------

By using the below syntax we could achieve the output as required.

UPDATE TestTable SET Gender = CASE Gender WHEN 'F' THEN 'M' ELSE 'F' END

• Function must return a value but in Stored Procedure it is optional( Procedure can return zero or n values).
• Functions can have only input parameters for it whereas Procedures can have input/output parameters .
• Functions can be called from Procedure whereas Procedures cannot be called from Function.
• Procedure allows SELECT as well as DML(INSERT/UPDATE/DELETE) statement in it whereas Function allows only SELECT statement in it.
• Procedures can not be utilized in a SELECT statement whereas Function can be embedded in a SELECT statement.
• Stored Procedures cannot be used in the SQL statements anywhere in the WHERE/HAVING/SELECT section whereas Function can be.
• Inline Function can be though of as views that take parameters and can be used in JOINs and other Rowset operations.
• Functions that return tables can be treated as another rowset. This can be used in JOINs with other tables.
• Exception can be handled by try-catch block in a Procedure whereas try-catch block cannot be used in a Function.
• We can go for Transaction Management in Procedure whereas we can't go in Function.