How Can I Query Foreign Key Relationships in SQL?

Retrieving Foreign Key Information in SQL

Understanding foreign key dependencies is crucial for database schema management. SQL provides a straightforward method to extract this information using the information_schema database metadata tables.

To list all foreign keys associated with a specific table, use this query:

<code class="language-sql">SELECT
    tc.table_schema,
    tc.constraint_name,
    tc.table_name,
    kcu.column_name,
    ccu.table_schema AS foreign_table_schema,
    ccu.table_name AS foreign_table_name,
    ccu.column_name AS foreign_column_name
FROM information_schema.table_constraints AS tc
JOIN information_schema.key_column_usage AS kcu
    ON tc.constraint_name = kcu.constraint_name
    AND tc.table_schema = kcu.table_schema
JOIN information_schema.constraint_column_usage AS ccu
    ON ccu.constraint_name = tc.constraint_name
WHERE tc.constraint_type = 'FOREIGN KEY'
    AND tc.table_schema = 'myschema'
    AND tc.table_name = 'mytable';</code>

Replace 'myschema' and 'mytable' with your desired schema and table names, respectively.

To find all tables referencing a given table as a foreign key, simply adjust the WHERE clause:

<code class="language-sql">WHERE tc.constraint_type = 'FOREIGN KEY'
    AND ccu.table_schema = 'myschema'
    AND ccu.table_name = 'mytable';</code>

This revised query will return all tables that utilize mytable in myschema as a foreign key.

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