What is a primary key in relational databases?

Answer 1

In a database , the primary key field defines the field that is unique and not null. Primary key is used to uniquely define a key.

Answer 2

A primary key is a set of one or more attributes that can uniquely identify tuples within the relation.

A Primary Key is made up of one or more fields or columns that are used to uniquely identify a record or row in a table. No two records can have the same primary key and the database manager will not allow that to happen

Primary key consists of column or columns whose value uniquely identifies a row.Following are the key feature of primary key

• It can't be null
• There can ONLY be one primary key defined on a single table.

A database designer choose this key to identifying unique records within a table. its values must not change.

a primary key tells you the difference between James smith and another James smith because one has a different number than the other.

The primary key is the field, or combination of fields, that uniquely identify each record in a table. It is usually the primary key that is stored in other tables (in which case it is called a "foreign key"), to find the record in the specified table. For example, a client might be identified by a field ClientId, which uniquely identifies each client. In the client table, this field would be called the "primary key"; if used in other tables to refer to a client, it is called a "foreign key".
We can uniquely identify the database by which attribute or set of attributes that is called the PRIMARY KEY.
it's basically a unique reference or ID (usually a number). You may need to create this in your database, or your dataset may already contain a unique ID field.
In a database , the primary key field defines the field that is unique and not null. Primary key is used to uniquely define a key.
It is used to uniquely identify each row in a table. The values must be unique and can not simply have NOT NULL.
To uniquely identify a tuple or row in database , primary key must be used. a primary key is used to uniquely identify a tuple.
A primary key is the unique identifier for a row in a database table. It is formed into a unique index constraint, so that access to the row in question can be quick. It is usually preferred by the optimizer as the primary join predicate. Presence of the primary key is usually a prerequiste for building a dynaset query, as opposed to a snapshot query, or for making an updateable view joining more than one table.
the powerful in a releation database management system such as MICROSOFT ACCESS from the ability to quikly find and bring together information stored in separate tables. in order for MICROSOFT ACCESS to work most efficiently each table in your database should include a field or set of fields that uniquely identifies each individual record stored in table. this often a unique idnetification number,such as an employee ID number or serial number. IN DATABASE TERMINOLOGY, this information is called<> of the table. MICROSOFT ACCESS uses primary key field to quikly associate data from multiple tables and bring the data together for you. make sure the values in this field will always be different for each record MICROSOFT ACCESS doesnt allow duplicate values in <>

Answer 3

To uniquely identify a tuple or row in database , primary key must be used. a primary key is used to uniquely identify a tuple.