7 Types of Keys in DBMS - A Glossary of Database Terms
Different Types of Keys in DBMS: Database management systems (DBMS) have existed for decades, and still, continue to be used for a wide range of applications. They are one of the most widely used technologies in modern computing with over one billion users worldwide. A database key is an identifier that uniquely identifies a row in the table containing data. Keys can also be referred to as primary keys and unique keys. A table’s primary key uniquely identifies each row in that table. Online Database Management Courses & Certifications Primary keys must not be nullable and can only contain blanks, numbers, or a combination of both. In this article we explore seven different types of keys in DBMS.
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What is a Database Key?
A database key is a unique identifier that uniquely identifies a row in the table containing data. Keys can also be referred to as primary keys and unique keys. A table’s primary key uniquely identifies each row in that table. Primary keys must not be nullable and can only contain blanks, numbers, or a combination of both.
The most common types of keys in DBMS are:
Unique Identifier
Object Table Key
Row Number
Sequence Number
Database ID
Database Name
Nullable
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Unique Identifier
A unique identifier is a primary key that will only have one value for a given row in the table. For example, the unique identifier would be the phone number. This uniquely identifies each row in the contacts table. A unique identifier must not be nullable and can only contain blanks, numbers, or a combination of both. For example, the unique identifier could be represented by 12345678901234
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Object Table Key
An object table key is a part of the primary key for an object table. It refers to the unique identifier within an object table. Object tables are used in relational databases to store objects such as people, locations, etc.
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Row Number
The row number is a unique identifier for a row in the table containing data. The row number can be used as a primary key or an index. Each table has their own unique row numbers that they use to identify each row in the table. An example of a table with a row number as its primary key would be an employee database that uses the employee ID as their primary key. If an employee’s ID was 12345, then their individual row number would be 1. This uniquely identifies each employee in that specific database.
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Sequence Number
A sequence number is a unique identifier that is used to define the place of each record in a table. The sequence number is an integer value, which increases with each new row inserted in the table. The first row of data inserted in a table will have a sequence number of one. A sequence number cannot be null and only contains digits from 1-9 and optionally letters A-Z. These values can be assigned to tables in many different ways.
For example, they can be generated by incrementing or adding a value or by using a key that has been assigned to the table with no modification. If your sequence number must increase with every new row inserted, consider using an auto-incrementing field as opposed to manually assigning your own sequence numbers.
Database ID
The database ID is a unique number that identifies the database. A database ID can only be used with a single database, and cannot be reused for other databases.
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Database Name
A database name is a key that uniquely identifies the data in a table. The database name is typically used to identify a unique data set with no duplicate records. The database name can also be used as a primary key, although it cannot be nullable and must only contain blanks, numbers, or a combination of both.
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Nullable
In database theory, a nullable key is one that can be set to NULL. A nullable primary key uniquely identifies each row in a table. A nullable primary key can contain blanks, numbers, or a combination of both. Nullable primary keys must not be null and cannot contain the letter "N". For example, an address key is not always unique and could have been set to NULL if there were no records for the address.
A key is an attribute of a database object that you can use to identify an object within a database. A key can be anything from an object ID to a sequence number or even a database name. Understanding how unique keys work and what they can be is essential to building a successful database.
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Frequently Asked Questions (FAQs)
A primary key is an identifier that uniquely identifies a row in the table containing data. Keys can also be referred to as primary keys and unique keys. A table’s primary key uniquely identifies each row in that table. Primary keys must not be nullable and can only contain blanks, numbers, or a combination of both.
A unique identifier uniquely identifies each row in the table containing data while a primary key can only contain blanks, numbers, or a combination of both. Unique identifiers must not be nullable and cannot allow duplicate values.
A database needs a Primary Key because it's the only field allowed to have values of NULL. All other fields must have valid values that cannot contain NULLs, otherwise, it will cause an error during entry or retrieval.
In Oracle: IDENTITY, NUMBER, SERIAL#, FIRST_NAME, LAST_NAME
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