Con este script podemos conocer cuales son las llaves foraneas (FK) existentes en una base de datos.
SELECT b.table_name, b.column_name, b.constraint_name,
b.referenced_table_name, b.referenced_column_name
FROM information_schema.table_constraints a
JOIN information_schema.key_column_usage b
ON a.table_schema = b.table_schema AND a.constraint_name = b.constraint_name
WHERE a.table_schema=database() AND a.constraint_type='FOREIGN KEY'
ORDER BY b.table_name, b.constraint_name;
Fuente: http://stackoverflow.com/questions/2470356/mysql-show-create-constraint
