Foreign key

As explained in Just Use Postgres!

A foreign key constraint requires values in a column or set of columns to match existing unique or primary-key values in a referenced table.

How Just Use Postgres! covers it

How deep it goes

Explains references, uniqueness requirements, index-based verification, failed inserts, and blocked deletes without covering cascading actions.

Examples

Demonstrates product reviews, customer accounts, invalid product identifiers, valid inserts, blocked account deletion, and soft deletion.

What it assumes

Requires related tables and a referenced primary or unique key, while demonstrating account-table creation before adding its foreign key.

What you can do after

Apply it via PostgreSQL ALTER TABLE statements and diagnose rejected inserts or deletes caused by broken references.

How it connects

Connects foreign keys with primary keys, unique constraints, table relationships, indexes, and data integrity.

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Also explained in

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  Grokking Relational Database DesignA foreign key constraint requires values in a child table's foreign key column to correspond to valid primary key values in a parent table and restricts operations that would break that correspondence.
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  Build Financial Software with Generative AI (From Scratch)A foreign key is a database constraint that references a key in another table to link related records and enforce valid relationships.
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  Learn SQL in a Month of LunchesA foreign key constraint is a database rule requiring designated column values to reference valid rows identified by a key in another table.
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  The Well-Grounded Python Developer: How the pros use Python and FlaskA foreign key is a column or set of columns that references a primary key in another relational database table to establish a relationship.
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  DuckDB in ActionA foreign key is a schema constraint requiring values in one table to reference corresponding values in another table.
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  Build Python Web Apps with StreamlitA foreign key constraint requires values in one table's column to correspond to existing values in a referenced table's key column.
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  100 SQL Server Mistakes and How to Avoid ThemA foreign key is a column or set of columns whose values reference a candidate key in another or the same table.
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  AI-Powered SearchA foreign key is a value or column in one table that references an entity or key in another table to link records.
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  Rust Servers, Services, and AppsA foreign-key constraint is a database rule requiring values in one table's column to reference valid values in another table's key column.
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  Effective Data AnalysisA foreign key is a column or set of columns whose values reference a key in another table to represent a relationship between rows.
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  Kafka Streams in Action, Second EditionA foreign key is a field whose value references a key in another table or record set.
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  Java Persistence with Spring Data and Hibernate epubA foreign key constraint enforces a referential relationship between values in one table and a candidate or primary key in another table.
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  PostgreSQL Mistakes and How to Avoid ThemA foreign key relationship is a referential association in which columns in one table identify rows in another input table.
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  Starting Data Analytics with Generative AI and PythonA foreign key is a column or set of columns whose values reference identifying values in another dataset's primary key.
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  Django in ActionA foreign key relationship is a database relationship in which records in one table reference a record in another table through a foreign key.
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  .NET in Action, Second EditionA foreign key is a relational-database column or set of columns whose values reference a key in another table.
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  Unit Testing Principles, Practices, and PatternsA foreign key constraint requires values in one database column or set of columns to correspond to valid values in another table.

Compare how 18 books explain foreign key →

Related concepts

• primary keyuses · A primary key is a designated column or attribute, or combination of them, that uniquely identifies each row or item in a table or data store.
• constraintkind of · A constraint is a condition or rule that restricts the permissible states, values, actions, or solutions in a system or problem.
• on delete cascadeconfigured by · ON DELETE CASCADE is a relational foreign-key action that automatically deletes referencing rows when their referenced row is deleted.
• referential integrityimplements · Referential integrity is the database property that references between related records correspond to valid existing keys or records.
• joinused by · A join is an operation that combines records or rows from multiple data sources according to specified matching conditions or relationships.
• schemapart of · A data schema is a formal specification of the structure, fields, types, relationships, and constraints of data.

This explainer was generated by Manning's knowledge graph from the text of Just Use Postgres!. The section links point to the parts of the book it draws on.