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Questions and Answers
What is the purpose of a primary key in a relational database?
What is the purpose of a primary key in a relational database?
How many primary keys can a table have?
How many primary keys can a table have?
What is the main function of foreign keys in a relational database?
What is the main function of foreign keys in a relational database?
What constraint applies to primary keys in a relational database?
What constraint applies to primary keys in a relational database?
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Which type of key ensures data integrity by preventing orphaned records?
Which type of key ensures data integrity by preventing orphaned records?
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Can foreign keys have duplicate values in a relational database?
Can foreign keys have duplicate values in a relational database?
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What is the purpose of primary keys in a relational database?
What is the purpose of primary keys in a relational database?
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Which constraint prohibits primary keys from having duplicate values?
Which constraint prohibits primary keys from having duplicate values?
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What is the main role of foreign keys in relational databases?
What is the main role of foreign keys in relational databases?
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Which feature distinguishes foreign keys from primary keys?
Which feature distinguishes foreign keys from primary keys?
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How do primary keys contribute to maintaining data integrity?
How do primary keys contribute to maintaining data integrity?
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In the context of relational databases, what role do foreign keys play in establishing connections between tables?
In the context of relational databases, what role do foreign keys play in establishing connections between tables?
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Study Notes
Primary Key vs. Foreign Key
In a relational database, keys help create structure by identifying data and defining relationships between tables. Two types of keys are primary keys and foreign keys.
Definition
Primary keys are columns in a table that uniquely identify the information in rows or tuples. Each table has just one primary key, which can have several attributes and is used to identify information within the table.
Foreign keys are columns that reference the primary key of another table, creating a link between them. Unlike primary keys, tables can have more than one foreign key, and they can reference more than one table.
Purpose
Primary keys ensure unique row identification in a table, making it easier to find and access specific information. They are a type of unique key that cannot have null values, and they are used to identify unique entries in a table.
Foreign keys, on the other hand, are used to establish a relationship between two tables by referencing the primary key or a unique key of another table. They ensure the integrity of data by preventing orphaned records, which is a record that has no connection to any other record in the database.
Uniqueness
Primary keys must be unique within a table and cannot contain null values, ensuring each row has a unique identifier. This uniqueness is enforced by the database management system.
Foreign keys can have duplicate values, but they must reference a primary key or unique key in another table. This link ensures the referenced table is consistent with the parent table.
Constraints
Primary keys have constraints that prevent duplicate values and enforce uniqueness. They cannot contain null values, which means each row must have a unique primary key.
Foreign keys also have constraints, such as referential integrity, which ensures that the data in the child table is consistent with the parent table's primary key. They can contain null values, which allows for more flexibility in the database.
Relationship between Tables
Parent tables, which are referenced by other tables, use primary keys. These primary keys are then used as foreign keys in child tables, ensuring a link between the two tables.
In summary, primary keys and foreign keys are essential in relational databases. Primary keys provide unique identification for rows within tables, while foreign keys create relationships between tables by referencing primary keys. Both keys play a crucial role in maintaining data integrity and structure in a database.
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Description
Learn the distinctions between primary keys and foreign keys in relational databases, including their definitions, purposes, uniqueness, constraints, and relationships between tables. Explore how primary keys uniquely identify rows within tables, while foreign keys establish connections and maintain data integrity.
