When Should You Use Primary and Foreign Keys for Joining Tables?

When Primary-Foreign Key Relations Are Essential in Joining Tables

While it's possible to join tables based on common columns, a primary-foreign key relationship serves a crucial purpose beyond facilitating joins.

Data Consistency Enforcement

Primary and foreign keys are designed to maintain data consistency.

• Primary keys: Ensure the uniqueness of values within a column. Without primary keys, it becomes impossible to differentiate between rows with identical values, leading to data integrity issues.
• Foreign keys: Establish a relationship between tables, ensuring that data references external entities that actually exist. This prevents "orphaned" records that point to non-existent entities.

Example of Data Inconsistency

Consider the example tables:

test1 (id, lname, fname, dob)
-- no primary and foreign key and not unique
-- (no constraints)

test2 (id, native_city)
-- no relations and no constraints

In this scenario, it's possible to join these tables based on the id column. However, without primary and foreign keys:

• Rows in test1 may have duplicate id values, making it difficult to identify specific records.
• Records in test2 may reference id values that do not exist in test1, leading to incorrect or incomplete data.

Conclusion

Primary-foreign key relations provide an additional layer of data integrity in addition to enabling joins. They prevent data corruption, ensure data relationships are maintained, and facilitate accurate and consistent data manipulation.

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