What is a composite key? composite vs super?

A composite key is the combination of one and more attribute which can uniquely identify a tuple value.

For example: if a student relation has attribute student id, student name, student class, student project id. The data of this relation is given below.

Table: Student

student idstudent namestudent classstudent project id

Here in the above table we can don’t have any unique column or candidate key which can uniquely identify the tuple value so, here we need to join two column value or attribute value to make a key which can easily identify the tuple in the above-given relation. So, we make student id and student as a primary key of this table and this primary key is also known as a composite key of this table.

What is the difference between the composite key and super key?

If you will see the definition of a super key which says that the combination of one and more attribute uniquely identifies a tuple value is called a super key you will confuse it with the composite key definition which is just looking similar at one glance.

But it is not like this, there is a difference between composite key and super key. In super key, the combination attributes have at least one candidate key which could be a primary as well as a unique key. But when we don’t have a candidate key in our table then we have to make a set of combine attribute which can easily identify a tuple uniquely. And now this combined key is called a composite key.

A candidate key is also known as minimal super key but in case of the composite key, there is no candidate key in the table.


When we are in a situation where we are unable to identify a tuple value uniquely with the help of one single column or we don’t have a candidate key or primary key in our table then we need to combine more than one attribute or column to make a primary key which can fetch thee tuple result, this type of primary key is known as composite key. We can say that super key is also a composite key but there is some minor difference between them.

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What is the null value in DBMS & problems with null? 2019

A null is basically used to represent the unknown and missing values. But it does not mean that the null value is equivalent to zero or a blank text string. See the example below for the same.

Table: Client

Client IDFirst NameMiddle initialLast NameCityCountry
2MaryNulllevisWiselandEast Midlands
4HalkNullJamurSillyvelly Null
5YenNullhuiNewcity North Brazil

How null values are created or inserted into the database?

It is good to have null values in the table whenever they are just for showing purpose like Middle name or stating some information. As you can see in the above client table null is useful to show the middle initial field and in the country field. If we want to use this null in a proper way then we should know the reason for their occurrence.

The very first reason for null values could be a manmade error. As while entering the data in the table, we forget to ask a particular client say John that which country does he live in. thus this missing data will be shown including a null value. You can see the country column for john in the above table.

There could be lots of reasons to fill a field with the value null. The value has not been defined for that field could be one of the reason. Let’s understand this scenario with an example related to the above table. Assume that we asked for john about his country information he is living in but unfortunately he does not know his country name and you also don’t have any idea about his country then we have to set a null value in his country column.

There could be another case where we need to insert the null value for a field. For example, in a company, an employee is working in both day and night shift, there are the fields total hour worked for the day and night shift both. Assume that he is at night shift for one month then his total hour worked in day shift will be always null for one month. So, in this case, null value come as per the condition.

Problems with null:

In general null value does not impact on anything until it is used just for showing the status of any field. But once that field is used in mathematical calculation with some other logical field then it can impact on the outcome result.

(50 x 3) + 10 = 160
(Null x 4) + 25 = Null
(20 x Null) + 500 = Null

With the help of below product table, you can see the impact of null value to a mathematical calculation.

Table: Product

Product CodeProduct NameProduct Category PricestockStockValue
1Fight with TruthBooksNull10Null
2 Fight with Truth Books30.955154.75
328 LEDNull120NullNull
4HP Printer Ink TankNull7010700.00
5Videocon LCD with home theaterAudio/Visual90NullNull
6Hard Disc 1TbDevice5515825.00

You can easily understand the problems due to null value by inspecting the value of above product table. Here stock value is derived by multiplication of price and stock field like[Price*stock]. So, for product 1 where the price is null, the stock value will always show null.

This problem can be more critical when you need to calculate the total value of all the item which are kept current in stock then you can not get an accurate result for the same.

to address this problem you need to make sure that price and stock field can’t be assigned as null.

See another example where null value is affecting an aggregate function.

Null values will also affect aggregate function that incorporates the value of a given field. If we were using an aggregate function, for example, a count function, the result will always contain a null if the field contains a null. The table below shows the results of performing a summary calculation that will count the number of occurrences of a category in the products table.

Let’s take an aggregate function which is counting the Product category column.

Category calculas

CategoryDescriptionTotal no. of Occurrences

After applying the aggregate function we can see the effect of null value clearly.

Count ProductCategory

Here in the result of category calculus, we can observe that the occurrence of the unspecified category is 0, whereas if we see the product table then we can easily find that there are two product which does not show any category.


So, in this blog, you have learned how the null value inserted in the database table. It can be entered by human mistake and some time data is unknown at present and we leave that field and by default, it is filled with null. And some time information does not match a particular column and thus filled with null. And you have also read the effect of these null value in mathematical operation and aggregate function.

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Research Paper on effective email marketing using optimized email cleaning process.

Hello Friends,

I am going to write this blog post especially for those who are pursuing M-tech(Master in Technology) or planning to pursue the same. As this research is based on achieving the effective email marketing using optimized email cleaning process.

There are not many research paper have been published on effective email marketing as this is becoming a new area of research. Email marketing has become a popular way to do online marketing as it has less investment and more profit.

You can download the research paper on effective email marketing using optimized email cleaning process below for free of cost. Here you can get both review and research paper both.

Review & Research Paper

You will not get more research paper over this topic as this is a new current in the research field and now slowly and slowly scholars are attracting towards this topic of effective email marketing and optimized cleaning process.

there are n numbers of ESP(Email Service Provider) and an equivalent number of email cleaning services. Most of them are offering a bulk range of cleaning and sending emails for free of cost.

Though ESP is capable of sending a bulk of emails with the help of SMTP server either with own or with a third party SMTP server. But still, users face various problems while using these ESP and Email cleaning service to achieve effective email marketing.

The biggest reason behind this problem is not to follow an effective email sending procedure which is usually documented by most of the ESP. And a similar case is with the email cleaning process.

Now, if you have decided to research either in Effective email marketing or optimized email cleaning procedure then you have to go through the internal procedure architecture of both.

Direction for research over effective email marketing.

As for effective email marketing, you can have research over ESP which will be new research in this area. How ESP can be effectively used to get effective email marketing or an effective email campaign.

You can research all possible common problems using ESP which can be easily done with a data mining technique over ESP data.

Here you can compare problems while sending the email campaign without best email sending practice and sending the email campaign with best email sending practice.

You can reach over SMTP suspension problem which is the most common and complex problem while doing the email marketing.

Direction for research over effective email cleaning process to achieve effective email marketing.

If you want to research over email verification then you would need to create an email cleaning algorithm code and then you would need to use an ESP to send the email campaign to your clean list and then you can compare this either with a standard result or you can use a trial of other email cleaning service and then you can compare it with your cleaning result.

Probably if you will search the email cleaning research paper then most of the time you will find the paper where email addresses are to be filtered from an email sent or received.

email domain and email content are two most important parameter to decide your email landing in a mailbox. If everything goes fine then your email land in user’s inbox folder else either it lands in the or rejected or bounced.

My research paper would be your base paper and then you can also collect relevant topic paper, you can also select a few papers from my research paper citation which is given at last. Then on the basis of all these papers, you will first make your review paper and then result in a paper at last after all execution work is done.


Effective email marketing, email verification, ESP are a new area of research which can enhance the Power of online marketing as this has been the future of today and will be surely enhanced with some updating. we can achieve effective email marketing with the help of best email sending practice and best email cleaning service or procedure. If you want to make research over these fields then you can either research over ESP relevant area like problems using ESP, Facts of a free trial, or email verification algorithm which should be cost effective too.

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Have a great time!