

In a database, you have entities (which have attributes), and relationships between those entities. Managing them is key to preventing chaos from engulfing your database, which is where the concept of keys comes in. These unique identifiers enable you to pick specific rows in an entity set, as well as define their relationships to rows in other entity sets, allowing your database to handle complex computations.
Let’s explore keys in DBMS (database management systems) in more detail, before digging into everything you need to know about the most important keys – primary keys.
Understanding Keys in DBMS
Keys in DBMS are attributes that you use to identify specific rows inside a table, in addition to finding the relation between two tables. For example, let’s say you have a table for students, with that table recording each student’s “ID Number,” “Name,” “Address,” and “Teacher” as attributes. If you want to identify a specific student in the table, you’ll need to use one of these attributes as a key that allows you to pull the student’s record from your database. In this case “ID Number” is likely the best choice because it’s a unique attribute that only applies to a single student.
Types of Keys in DBMS
Beyond the basics of serving as unique identifiers for rows in a database, keys in DBMS can take several forms:
- Primary Keys – An attribute that is present in the table for all of the records it contains, with each instance of that attribute being unique to the record. The previously-mentioned “ID Number” for students is a great example, as no student can have the same number as another student.
- Foreign Key – Foreign keys allow you to define and establish relationships between a pair of tables. If Table A needs to refer to the primary key in Table B, you’ll use a foreign key in Table A so you have values in that table to match those in Table B.
- Unique Key – These are very similar to primary keys in that both contain unique identifiers for the records in a table. The only difference is that a unique key can contain a null value, whereas a primary key can’t.
- Candidate Key – Though you may have picked a unique attribute to serve as your primary key, there may be other candidates within a table. Coming back to the student example, you may record the phone numbers and email addresses of your students, which can be as unique as the student ID assigned to the individual. These candidate keys are also unique identifiers, allowing them to be used in tandem with a primary key to identify a specific row in a table.
- Composite Key – If you have attributes that wouldn’t be unique when taken alone, but can be combined to form a unique identifier for a record, you have a composite key.
- Super Key – This term refers to the collection of attributes that uniquely identify a record, meaning it’s a combination of candidate keys. Just like an employer sifting through job candidates to find the perfect person, you’ll sift through your super key set to choose the ideal primary key amongst your candidate keys.
So, why are keys in DBMS so important?
Keys ensure you maintain data integrity across all of the tables that make up your database. Without them, the relationships between each table become messy hodgepodges, creating the potential for duplicate records and errors that deliver inaccurate reports from the database. Having unique identifiers (in the form of keys) allows you to be certain that any record you pull, and the relationships that apply to that record, are accurate and unrepeated.
Primary Key Essentials
As mentioned, any unique attribute in a table can serve as a primary key, though this doesn’t mean that every unique attribute is a great choice. The following characteristics help you to define the perfect primary key.
Uniqueness
If your primary key is repeatable across records, it can’t serve as a unique identifier for a single record. For example, our student table may have multiple people named “John,” so you can’t use the “Name” attribute to find a specific student. You need something unique to that student, such as the previously mentioned ID number.
Non-Null Values
Primary keys must always contain a value, else you risk losing records in a table because you have no way of calling upon them. This need for non-null values can be used to eliminate some candidates from primary key content. For instance, it’s feasible (though unlikely) that a student won’t have an email address, creating the potential for null values that mean the email address attribute can’t be a primary key.
Immutability
A primary key that can change over time is a key that can cause confusion. Immutability is the term used for any attribute that’s unchanging to the point where it’s an evergreen attribute that you can use to identify a specific record forever.
Minimal
Ideally, one table should have one attribute that serves as its primary key, which is where the term “minimal” comes in. It’s possible for a table to have a composite or super key set, though both create the possibility of confusion and data integrity issues.
The Importance of a Primary Key in DBMS
We can distill the reason why having a primary key in DBMS for each of your tables is important into the following reasons:
- You can use a primary key to identify each unique record in a table, meaning no multi-result returns to your database searches.
- Having a primary key means a record can’t be repeated in the table.
- Primary keys make data retrieval more efficient because you can use a single attribute for searches rather than multiple.
Functions of Primary Keys
Primary keys in DBMS serve several functions, each of which is critical to your DBMS.
Data Identification
Imagine walking into a crowded room and shouting out a name. The odds are that several people (all of whom have the same name) will turn their heads to look at you. That’s basically what you’re doing if you try to pull records from a table without using a primary key.
A primary key in DBMS serves as a unique identifier that you can use to pull specific records. Coming back to the student example mentioned earlier, a “Student ID” is only applicable to a single student, making it a unique identifier you can use to find that student in your database.
Ensure Data Integrity
Primary keys protect data integrity in two ways.
First, they prevent duplicate records from building up inside a single table, ensuring you don’t get multiple instances of the same record. Second, they ensure referential integrity, which is the term used to describe what happens when one table in your database needs to refer to the records stored in another table.
For example, let’s say you have tables for “Students” and “Teachers” in your database. The primary keys assigned to your students and teachers allow you to pull individual records as needed from each table. But every “Teacher” has multiple “Students” in their class. So, your primary key from the “Students” table is used as a foreign key in the “Teachers” table, allowing you to denote the one-to-many relationship between a teacher and their class of students. That foreign key also ensures referential integrity because it contains the unique identifiers for students, which you can look up in your “Students” table.
Data Retrieval
If you need to pull a specific record from a table, you can’t rely on attributes that can repeat across several records in that table. Again, the “Name” example highlights the problem here, as several people could have the same name. You need a unique identifier for each record so you can retrieve a single record from a huge set without having to pore through hundreds (or even thousands) of records.
Best Practices for Primary Key Selection
Now that you understand how primary keys in DBMS work, here are some best practices for selecting the right primary key for your table:
- Choose Appropriate Attributes as Candidates – If the attribute isn’t unique to each record, or it can contain a null value (as is the case with email addresses and phone numbers), it’s not a good candidate for a primary key.
- Avoid Using Sensitive Information – Using personal or sensitive information as a primary key creates a security risk because anybody who cracks your database could use that information for other purposes. Make your primary keys unique, and only applicable, to your database, which allows you to encrypt any sensitive information stored in your tables.
- Consider Surrogate Keys – Some tables don’t have natural attributes that you can use as primary keys. In these cases, you can create a primary key out of thin air and assign it to each record. The “Student ID” referenced earlier is a great example, as students entering a school don’t come with their own ID numbers. Those numbers are given to the student (or simply used in the database that collects their data), making them surrogate keys.
- Ensure Primary Key Stability – Any attribute that can change isn’t suitable for use as a primary key because it causes stability issues. Names, email addresses, phone numbers, and even bank account details are all things that can change, making them unsuitable. Evergreen and unchanging is the way to go with primary keys.
Choose the Right Keys for Your Database
You need to understand the importance of a primary key in DBMS (or multiple primary keys when you have several tables) so you can define the relationships between tables and identify unique records inside your tables. Without primary keys, you’ll find it much harder to run reports because you won’t feel confident in the accuracy of the data returned. Each search may pull up duplicate or incorrect records because of a lack of unique identifiers.
Thankfully, many of the tables you create will have attributes that lend themselves well to primary key status. And even when that isn’t the case, you can use surrogate keys in DBMS to assign primary keys to your tables. Experiment with your databases, testing different potential primary keys to see what works best for you.
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The Open Institute of Technology (OPIT) is turning two! It has been both a long journey and a whirlwind trip to reach this milestone. But it is also the perfect time to stop and reflect on what we have achieved over the last two years, as well as assess our hopes for the future. Join us as we map our journey over the last two years and look forward to future plans.
July 2023: Launching OPIT
OPIT officially launched as an EU-accredited online higher education institution in July 2023, and offered two core programs: a BSc in Modern Computer Science and an MSc in Applied Data Science and AI. Its first class matriculated in September of that year.
The launch of OPIT was several years in the making. Founder Riccardo Ocleppo was planning OPIT ever since he launched his first company, Docsity, in 2010, an online platform for students to share access to educational resources. As part of working on that project, Ocleppo had the chance to talk to thousands of students and professors and discovered just how big a gap there is between what is taught in universities today and job market demands. Ocleppo felt that this gap was especially wide in the field of computer science, and OPIT was his concept to fill that gap.
The vision was to provide university-level teaching that was accessible around the world through digital learning technologies and that was also affordable. Ocleppo’s vision also involved international professors and building strong relationships with global companies to ensure a truly international and fit-for-purpose learning experience.
One of the most important parts of launching OPIT was the recruitment of the faculty of professors, which Ocleppo was personally involved in. The idea was to build a roster of expert teachers and professionals who were leaders in the field and urge them to unite the teaching fundamentals with real-world applications and experience. The process involved screening more than 5,000 CVs, interviewing over 200 candidates, and recruiting 25 professors to form the core of OPIT’s faculty.
September 2023: The Inaugural Cohort
When OPIT officially launched, its first cohort included 100 students from 38 different countries. Divided between the BSc and MSc courses, students were also allowed to participate in one of two different tracks. Some chose the standard track to accommodate their existing work commitments, while others chose to fast-track to complete their studies sooner.
OPIT was pleased with its success in making the courses international and accessible, with notable representation from Africa. In the first cohort, 40% of MSc students were also from non-STEM fields, showing OPIT’s success at engaging professionals looking to develop skills for the modern workplace.
July 2024: A Growing Curriculum
Building on this initial success, in 2024, OPIT expanded its academic offering to include a second BSc program in Digital Business, and three new MSc programs in Digital Business & Innovation, Responsible Artificial Intelligence, and Enterprise Cybersecurity. These were all offered in addition to the original two programs.
The new course offerings led to total student numbers growing to over 300, hailing from 78 different countries. This also led to an expansion of the faculty, with professionals recruited from major business leaders such as Symantec, Microsoft, PayPal, McKinsey, MIT, Morgan Stanley, Amazon, and U.S. Naval Research. This focus on professional experience and real-world applications is ideal for OPIT as 80% of the student body are active working professionals.
January 2025: First Graduating Class
OPIT held its first-ever graduation ceremony in Valletta, Malta, on March 8, 2025. The ceremony was a hybrid event, with students attending both in person and virtually. The first graduating class consisted of 40 students who received an MSc in Applied Data Science and AI.
OPIT’s MSc programs include a capstone project that sees students apply their learning to real-world challenges. Projects included the use of large language models for the creation of chatbots in the ed-tech field, the digitalization of customer support processes in the paper and non-woven industry, personal data protection systems, AI applications for environmental sustainability, and predictive models for disaster prevention linked to climate change. Since many OPIT students realized their capstone projects within their organizations, OPIT also saw itself successfully facilitating digital innovation in the field.
July 2025: New Learning Environments
The next step for OPIT is not just to teach others how to leverage AI to work smarter, but to start applying AI solutions in our own business environment. To this end, OPIT unveiled its OPIT AI Copilot at the Microsoft AI Agents and the Future of Higher Education event in Milan in June 2025.
The OPIT AI Copilot is a specialist AI Agent designed to enhance learning in OPIT’s fully digital environment. OPIT AI Copilot acts as a personal tutor and study companion, and but rather than being trained on the World Wide Web, it is specifically trained on OPIT’s educational archive of around 3,500 hours of lectures and 3,000 proprietary documents.
The OPIT AI Copilot then provides real-time, personalized guidance that adapts to where the student is in the course and the progress they have shown in grasping the material. As well as pulling from existing materials, the OPIT AI Copilot can generate content to deepen learning, such as code samples and practical exams. It can also answer questions posed by the students with answers grounded in the official course material. The tool is available 24/7, and also has an intelligent examination mode, which prevents cheating.
In this way, OPIT AI Copilot enriches the OPIT learning environment by providing students with 24/7 personalized support for their learning journey, ideal for busy professionals balancing work and study. It is a step towards facing the challenge of “one-size-fits-all” education approaches that have plagued learning institutions for millennia.
September 2025: A New Cohort
On the heels of the OPIT AI Copilot launch, OPIT is excited about recruiting its next round of students, with applications open until September 2025. If you are interested in joining OPIT, you can learn more about its courses here.

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