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What is the relationship between Primary key and foreign key?

The relationship between a primary key and a foreign key is a fundamental concept in relational database design. It is used to establish relationships between tables and enforce data integrity. Here are the key points:

Primary Key:

  1. A primary key is a column or a set of columns in a table that uniquely identifies each row in the table.
  2. It ensures the uniqueness and integrity of data within the table.
  3. There can be only one primary key in a table.
  4. The primary key of one table can be referenced in another table as a foreign key.

Foreign Key:

  1. A foreign key is a column or a set of columns in a table that references the primary key of another table.
  2. It establishes a relationship between two tables based on the values of the foreign key column(s).
  3. The foreign key column(s) in a table refers to the primary key column(s) of another table.
  4. It helps maintain referential integrity, ensuring that the values in the foreign key column(s) of a table correspond to existing values in the referenced primary key column(s) of the related table.
  5. A foreign key can have NULL values, indicating that a row may not have a corresponding related row.

The relationship between a primary key and a foreign key can be summarized as follows:

  1. The primary key in one table becomes the target for the foreign key in another table.
  2. The foreign key refers to the primary key to establish a relationship between the two tables.
  3. This relationship allows tables to be connected and linked together, forming meaningful associations between the data.
  4. The foreign key ensures referential integrity by enforcing constraints on the values that can be inserted or updated in the foreign key column(s).

By using primary key and foreign key relationships, we can create relational databases that represent the logical connections between entities, ensuring data consistency, and enabling data retrieval through joins and related operations.

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