foreign key造句怎么写

The logical model for a relational database normalizes the entities and relationships into tables with foreign key constraints.

ON DELETE CASCADE—When a record is deleted from the parent table, all records in the child table with matching foreign key values are also deleted.

Because the values in the aforementioned columns are not unique, a separate ID represents each quadruple (label, description, begin_production, end_production) and is a foreign key in other tables.

Controlling the ETL work in this manner can be useful for guaranteeing the proper sequence for loading data warehouse tables that contain primary or foreign key dependencies.

This is a classic one-to-many relationship, and would usually be modeled for a database as a user table and a phone number table, where the phone number table contains a foreign key to the user table.

When ON delete set NULL is active, when a record is deleted from the parent table, all records in the child table with matching foreign key values are set to NULL.

A relationship between the main foreign key constraint graph.

Fortunately, with a basic understanding of the primary key and foreign key strategy employed, you can find anything you want.

If informational check constraints exist on the primary key column, you should explicitly specify informational check constraints on their corresponding foreign key columns. For example.

This will not affect the referential integrity or primary-foreign key relationships between the tables in the membership database.

For this example, consider the creation of a foreign key for every association end to occur with a multiplicity of "one". As a consequence, two things may occur.

For one-to-one associations, developers have to select which end of the association holds the foreign key that represents the other end (this gets propagated down to the database schema).

Specifications for all primary keys and foreign keys.

When we are able to relate without ambiguity any association end to a foreign key, we can apply the correspondence to specify to which primary key the foreign key refers.

In general, that data would live in a child table with a foreign key relation to the table contacts.

When an ON delete CASCADE rule is active, all records in the child table with matching foreign key values are deleted when a record is deleted from the parent table.

The article shows one solution that we add triggers to simulate the primary key and foreign key, and then realize cascade update.

When creating a foreign key, Informix automatically creates a B-Tree index on the child table when creating a foreign key.

Having the database generate values for the primary key for a table (and by extension, any foreign key values for related tables) eliminates the burden from the application from having to do so.