What is Foreign Key?
Foreign key is used in relational database context. It refers to one or a combination of multiple fields in an existing table, which can be used as a bridge to link to another table. A foreign key in the current table should be the primary key of the other table to be linked. A foreign key is often referred as a join key (in the context of two tables to be joined together), or a lookup key (in the context of looking up a reference value from another table).