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 The Oracle FOREIGN KEY Constraint      [Return To Index] Jump to:  


In its simplest form, a foreign key is a referential constraint between two tables. A foreign key constraint validates the values of an INSERT or UPDATE against the values in another column, either in a different table or another column in the same table. Generally, though, a foreign key is a field (or fields) that points to the primary key of another table.

A foreign key can also be described as a column in a table that does NOT uniquely identify rows in that table, but is used as a link to matching columns in other tables to indicate a relationship.

A foreign key always defines a parent/child relationship. The "parent" is the column that is referenced in the foreign key and the "child" is the column or columns that contain the foreign key constraint.

Example Syntax:
In this example, the Customer_SID column in the ORDERS table is a foreign key pointing to the SID column in the CUSTOMER table:

(Order_ID integer primary key,
Order_Date date,
Customer_SID integer references CUSTOMER(SID),
Amount double);
Amount double);

You may also want to see additional information in the entry on the CONSTRAINT clause.

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