Database – What is a Primary Key?

A primary key is a unique column in relational database tables that uniquely identifies each table record.

This column can only accept valid values and helps quickly parse data within the table.

A primary key can also be utilized to generate foreign keys and establish relationships between tables.

Definition

A primary key is a column in a database table that uniquely identifies each row. It cannot be NULL and must contain unique values that cannot be duplicated within one column or any combination of columns.

Database tables may have only one primary key, or multiple columns that function as a composite key. The choice of primary key can be determined by an administrator’s preference for its identifier; alternatively, it could be specified as a foreign key to another table to create a reference to it.

Selecting a primary key can be challenging, as it must meet several requirements. It must be unique – such as not being the same as another ZIP code, email address or employer – and short enough so that it can be processed quickly by the database management system.

Furthermore, the identifier must be a number and not a character. Using numbers instead of characters allows the database management system to process it faster, particularly when used for lookups and comparisons.

It should also be simple to read and remember. For instance, a national identification number could serve as an appropriate choice when creating a database of people with that country’s citizenship.

When selecting a primary key, keep in mind that different databases have distinct needs. It’s essential to determine what the identifier will be used for before selecting it so you can design your database with an optimal identifier.

For instance, a database of car parts might require each part to be uniquely identified. In such cases, either the engine_ID or body_ID can be utilized as the primary key.

A social security number is another great choice for a database of individuals. It’s an actual-world identifier that can evolve over time and it can be utilized to establish connections with other databases or people outside the database.

Furthermore, a social security number can be generated automatically when adding a new record to the database. This may be suitable for small amounts of non-sensitive data that won’t require much processing power.

User

The primary key on a table is the name assigned to a special column that uniquely identifies each record within it. It’s also tied into the database where the table resides and used for creating references between tables.

A primary key can be composed of either one or multiple columns and can contain various data types. Numbers are the preferred choice, though characters and other data types can also be utilized. The value of this primary key must remain unique and unalterable since it will be utilized for lookups and comparisons between records in different tables.

Selecting a suitable primary key depends on the nature and purpose of your table’s data. If it changes frequently, then opting for a shorter key might be preferable; similarly, if creating a new key from scratch, using numbers might be more suitable.

In general, primary keys should be generated using real-world observables or attributes – this is known as a natural primary key.

Natural primary keys include street addresses, driver’s license numbers, and Social Security numbers. Most people deal with these identifiers daily in their daily lives.

These identifiers make an ideal primary key, as they’re unique and assigned by the government. Unfortunately, they have two issues: they can change over time and represent many people.

Given these issues, deciding whether a natural or surrogate key should be used as your table’s primary key is essential. For instance, if you need to identify customers based on their account numbers, a natural key would benefit more than one generated through surrogacy.

However, a natural key may not be sufficient if you need to identify a customer by their email address. That is because one email address can be associated with multiple customers, and it’s difficult to know which ones belong to each one.

Another issue is the maintenance of natural primary keys. If a primary key change or is reassigned by the government, you might need to create new columns in your database to store the updated data – an extensive and time-consuming process.

Purpose

A primary key in a table refers to a column or group of columns that uniquely identifies each row. This can be either single (with one column) or composite (with multiple columns).

The primary key must be set when adding a table to an Access database. This allows for linking data within the table with information in other tables using a foreign key.

Relational databases enable tables to be linked together via foreign keys. A foreign key column in one table links to a column with unique values in another, creating an association between them.

A primary key is a combination of values in a row, such as an employee ID number or date/time that uniquely identify an individual record. A primary key column must have no null values and be as compact as possible to ensure its accuracy.

Natural primary keys, such as a student ID number or social security number, are frequently employed to uniquely identify each record. These keys come from real-world observables and attributes and tend to be more accurate than surrogate primary keys.

Surrogate keys differ from natural keys in that they are not automatically assigned to each record and can be altered at any time. For instance, if an employee moves to a different city, their primary key may no longer be accurate.

However, you can avoid this issue if you create an intelligent primary key that combines the employee ID number and city and state where a customer first ordered from you. This primary key can be used for sorting and filter records based on location or by year or month.

When managing a database with thousands of records, selecting an effective primary key is essential. The key should be compact and non-null and ensure its relevance remains constant over time.

Example

A primary key is a field or set of fields that uniquely identifies records in a table. They serve to create relationships between tuples within an RDBMS, serving also as the identifier for foreign keys within those relationships.

Keys can consist of one column or multiple columns. Usually, one or more columns is designated as the primary key. A composite key also exists which uses values from two or more columns to generate a unique identifier.

A table’s primary key must be unique across all records, ensuring that each record can be identified by its unique value and preventing duplicated values from appearing.

An RDBMS requires every table to have a primary key, and each tuple in a relation must have non-null value for this key. A primary key makes it straightforward to utilize, insert and access data stored within the table.

Ideal keys should be numeric or integer. A Hi/Lo algorithm can increase or generate values, providing fast and efficient data retrieval.

Many real-world observables and attributes, such as a student ID number or street address, can be used as primary keys. These identifiers can be generated automatically when a new record is inserted into a table or obtained from an existing record.

In some circumstances, using a natural key may not be possible for software development. In such instances, surrogate keys are preferred.

Surrogate keys are system-generated and business agnostic, providing a better framework for user interaction with data.

Natural keys can be laborious to create and maintain, so a surrogate key is often preferred. The primary key of a relation can be specified using either the PRIMARY KEY constraint at the table level or column level.

Before a candidate key can be chosen as the primary key of an entity, it must meet several criteria: it must be unique; accessible or insertable; not null during relation; non-repeating; and short in length.