foreign key


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foreign key

(database)
A column in a database table containing values that are also found in some primary key column (of a different table). By extension, any reference to entities of a different type.

Some RDBMSs allow a column to be explicitly labelled as a foreign key and only allow values to be inserted if they already exist in the relevant primary key column.

foreign key

In relational databases, it is a field in one table that is indexed in another. Foreign keys provide the building blocks for relating tables. For example, in a customer order table, the salesperson field might contain an employee number. That field would be a foreign key in the table, because the employee table would be indexed on employee number. See entity relationship model.


Foreign Keys
Note the "FK" indications in this Erwin entity relationship modeling program. Every foreign key is a field in one table that is indexed in another. (Example courtesy of Logic Works, Inc.)
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Information stored at the meta-level permits the implicit and dynamic definition of domain-dependent database schemas, including information about primary and foreign keys, which are essential for maintaining data consistency.
Ensure all primary keys, foreign keys, and referential integrity constraints are clearly set.
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will be retrieved later when the user starts to collect time study data and will be saved together with these data as a foreign key in the database.
Relationships can be represented either by using foreign keys or constructing new relations.
for a foreign key and 2) the designer selected a special value to represent null.
The INSERT rule indicates what will happen if you attempt to insert a value into a foreign key column without a corresponding primary key value in the parent table.
Many times, especially with a foreign key, a default value isn't wanted, so remember to delete anything that may be specified.
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Tubular lock abs with anodized finish, standard for divisional, with two pins, simple model, latch 90mm, foreign key and button internal lock, black.

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