1. What are differences between the DELETE and TRUNCATE statement?

2. What are the different subsets of SQL?

3. What do you mean by DBMS? The different types?

4. What do you mean by table and field in SQL?

5. What are the joins in SQL?

6. What is the difference between CHAR and VARCHAR2 datatype in SQL?

7. What is a Primary Key?

8. What are Constraints?

9. What is the difference between SQL and MYSQL?

10. What is a Unique Key?

11. What is a Foreign Key?

12. What do you mean by data integrity?

13. What is the difference between clustered and non clustered index in SQL?

14. Write a SQL query to display the current date?

15. What are the different types of joins?

16. What do you mean by Denormalization?

17. What are Entities and Relationships?

18. What is an Index?

19. Explain the different types of Index.

20. What is Normalization and what are the advantages?

21. What is the difference between the drop and Truncate commands?

22. Explain different types of Normalization.

23. What is ACID property in a database?

24. What do you mean by trigger in SQL?

25. What are the different operators available in SQL?

26. Are null values the same as zero or blank space?

27. What is the difference between cross join and natural join?

28. What is subquery in SQL?

29. What are the different types of a subquery?

30. List the ways to get the count of records in a table.

SELECT * FROM table1;
SELECT COUNT(*) FROM table1;

31. Write a SQL query to find the names of employees that begin with ‘A’

SELECT * FROM aTable WHERE name LIKE 'A%';

32. Write a SQL query to get the third highest salary of an employee from employee_table.

SELECT TOP 3 salary FROM employee_table;

33. What is the need for group functions in SQL?

34. What is a Relationship and what are they?

35. How can you insert NULL values in a column while inserting the data?

36. What is the main difference between ‘BETWEEN’ and ‘IN’ condition operators?

37. Why are SQL functions used?

38. What is the need of MERGE statement?

39. What do you mean by recursive stored procedure?

40. What is the CLAUSE in SQL?

41. What is the difference bewteen ‘HAVING’ CLAUSE and a ‘WHERE’ CLAUSE?

42. List ways in which Dynamic SQL can be executed?

43. What are the various levels of constraints?

44. How can you fetch common records from the two tables?

45. List some manipulation functions in SQL.

46. What are the different operators available in SQL?

47. What is an ALIAS command?

48. What are aggregate and scalar functions?

49. How can you fetch alternate records from a table?

50. Name the operator which is used in the query for pattern matching?

51. How can you select unique records from a table?

52. How can you fetch the first 5 characters of a string?

53. What is the main difference between SQL and PL/SQL?

54. What is a View?

55. What are Views used for?

56. What is a stored Procedure?

57. List some advantages and disadvantages of Stored Procedures?

58. List all the types of user-defined functions?

59. What do you mean by Collation?

60. What are the different types of Collation Sensitivity?

61. What are Local and Global variables?

62. What is Auto Increment in SQL?

63. What is a Datawarehouse?

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

65. What are STUFF and REPLACE function?

Links I used to answer these questions:

https://www.w3schools.com

https://www.wikipedia.org/

In this tutorial we will be using MYSQL Workbench. I will assume you already have MYSQL Workbench set up and are connected to it.

The update command is used to modify existing records in a table.

You can update two different ways. Either using a WHERE clause or without WHERE clause. Using the WHERE clause will allow you to select particular rows. If you don’t use it, all the rows will be changed.

To Start You Need To Select The Database

use sakila;

The above code will select the database called sakila.

If you want to see all the values of your rows use the SELECT clause.

SELECT * from film;

That selects all ( * ) the rows contained in the table film. This will allow you to preview your changes to make sure you’ve done everything accurately. This is an example of the output below.

Now we will change the lanugage_id of row 1 from 1 to 2. To do this we need to use the update command

UPDATE film SET language_id = 2 WHERE film_id = 1;

The above code will go to the film table and look where a film_id is equal to 1 and set that rows language_id to 2.

You can also do something else like the following

UPDATE film SET language_id = 2 WHERE rental_rate = 0.99;

That will change all the rows that have a rental_rate of 0.99. It will change their language_id to 2.

The code below will change all the row’s language_id to 1.

UPDATE film set language_id = 1;

As you can see now the language_id are all back to 1 like how we started.

That was a quick tutorial on using the UPDATE command in SQL.

What is the JRE?

What is the JDK?

What is the JVM?

What is a Singleton Class and whats the best way to implement one?

Can a semaphore act as a mutex?

If you were to use a set, how would you determine between a HashSet and a TreeSet?

Why should you avoid the finalize() method in the Object class? What are some alternatives?

Is an object a reference?

Assigning objects is pretty important in Java. In Java you have two different types of data types. primitive data types (byte, char, short, int, long, float, double, boolean) and you have reference data types. Objects are reference data types. The content of a reference data type is an address to where the data is stored.

In order to do this first we have to allocate the variable in memory.

// Assigning Objects
Cellphone android;

Above Cellphone is the class we are going to reference and android is the name of the variable that is going to hold the reference to the object.

// Referencing a new object
android = new Cellphone("Samsung");

Here we create a new object of the class called Cellphone. We then send it a parameter Samsung. Then the variable android is given a link to the new object we created.

We can also allocate more then one variable at the same time.

// Two References to a single object
Cellphone samsung1, samsung2;

To reference a new object to samsung1 we do

samsung1 = new Cellphone("Samsung");

Then to assign the reference in samsung1 to samsung2

samsung2 = samsung1;

Abstract and Interfaces are two important uses in Java Classes. Here are a few differences between the two of them. At the bottom I put an example of each one being used.

Abstract classes are allowed to have both abstract and non abstract methods. While interface methods are ONLY allowed to have abstract methods.

Abstract

abstract class LaptopsAbstract
{
    public void color(String aColor)
    {
        System.out.println("The laptop color is " + aColor);
    }

    abstract public void type(String aType);
}

Interface

interface LaptopInterface
{
    abstract public void color(String aColor);

    abstract public void type(String aType);
}

Abstract classes DO NOT support multiple inheritance. While Interface classes do allow it.

class Mac implements LaptopInterface, LaptopInterfaceTwo
{

When using Interface classes you have to implement. Using abstract classes you must extend.

Interface

class Mac implements LaptopInterface
{}

Abstract

class Acer extends LaptopsAbstract
{}

Abstract classes can have final, non final, static and non static variables. Interface has only static final variables.

Abstract

abstract class LaptopsAbstract
{
    String color = "black";
    Final int screenSize = 13;
}

Interface

interface LaptopInterface
{
     Static Final int screenSize = 13;
}

An Interface can only extend another interface. An Abstract can extend another class and implement multiple interfaces.

Interface

interface LaptopInterface extends LaptopInterfaceTwo
{}

Abstract

abstract class LaptopsAbstract extends OtherClass implements LaptopInterface
{}

Abstract can have private protected etc. methods. While Interface is only public by default.

Abstract

abstract class LaptopsAbstract
{
    private String color = "black";
}

Interface

interface LaptopInterface
{
    String color = "black";
}

Below is an example of extending Abstract classes

abstract class LaptopsAbstract
{
    private String color = "black";

    public void color(String aColor)
    {
        System.out.println("The laptop color is " + aColor);
    }

    abstract public void type(String aType);

    abstract public void screenSize(int screenSize);
}

class Acer extends LaptopsAbstract
{
    public void type(String aType)
    {
        System.out.println("The tpe of laptop is " + aType);
    }

    public void screenSize(int screenSize)
    {
        System.out.println("The screen size of the laptop is " + screenSize);
    }

    public static void main(String[] args) {
        LaptopsAbstract acer = new Acer();

        acer.type("Acer");
        acer.screenSize(17);
        acer.color("black");
    }
}

Below is an example implementing Interfaces

interface LaptopInterface
{
    String color = "black";

    abstract public void color(String aColor);

    abstract public void type(String aType);

    abstract public void screenSize(int screenSize);
}

class Mac implements LaptopInterface
{
    public void color(String aColor)
    {
        System.out.println("The color is " + aColor);
    }

    public void type(String aType)
    {
        System.out.println("The type is " + aType);
    }

    public void screenSize(int screenSize)
    {
        System.out.println("The screen size is " + screenSize);
    }

    public static void main(String[] args) {
        LaptopInterface aMac = new Mac();

        aMac.color("White");
        aMac.type("Mac");
        aMac.screenSize(13);
    }
}

This is an example of how to use methods in different classes.

Java methods are methods in a class used to perform actions.

They can either be static or public.

Static Methods can be accessed in a class without creating an object.

Below is an example on using a Static Method. I created a class called UsingClassMethods.

public class UsingClassMethods
{  

Then I created a static method called testStaticMethod.

    static void testStaticMethod()
    {

Finally I call the static method testStaticMethod from the main method.

testStaticMethod();

Below is the hole code put together.

public class UsingClassMethods
{  
    //Since this method is static it can be accessed in this class without creating an object of this class
    static void testStaticMethod()
    {
        System.out.println("This is called from a static method in UsingClassMethods\n");
    }

    public static void main(String[] args)
    {
        //This is called from a static method in this class, UsingClassMethods
            testStaticMethod();
    }
}

For Public Methods you need to create an object of the class to access them. Below is an example of an Object called testClassObject that uses the class UsingClassMethods.

        //This creates a new object of this class, UsingClassMethods
        UsingClassMethods testClassObject = new UsingClassMethods();

To access methods in an object you need to first write the object’s name with a dot or .

You can also create an object of a class and access it from another class in a different file. Below you can find my user file. This will be the class used to create an object. It contains a String name and two public methods. The first one setUsername to set the value and the following getUsername to retrieve the value.

//This is the User class as its own file
//It consists of a name string and two methods one to set it and one to retrieve it
public class User
{
    String name = "";

    public void setUsername(String tempName)
    {
        name = tempName;
        System.out.println("The string has been sent to the User class method setUsername\n");
    }


    public void getUsername()
    {
        System.out.println("This is from the User class method getUsername and this is the string sent from UsingClassMethods: " + name +"\n");
    }
}

Finally this is an example of using the User class as an object.

//Class Methods are used to call methods between different classes
public class UsingClassMethods
{
        //This creates an object of the class User called aUser
            User aUser = new User();
            System.out.println("This creates an object of a class called User\n");


        //This is calling the setUsername method from the object called aUser
            aUser.setUsername("Greg");


        //This calling the getUsername method from the object called aUser
            aUser.getUsername();
    }
}

A question to ask yourself. What is the difference between using static and public on methods?