Databases: Primary, Foreign and Alternate Keys
From GMOD
This introduces some terminology frequently used in relations databases.
In a database table, certain columns are keys. Keys help identify rows / records and link records together.
Primary Key
Uniquely identifies a record/row/object/person.
Alternate Key
Also uniquely identifies a record/row/object/person
Foreign Key
Related tables are linked together by taking the primary key from one table and placing in the related table. The primary key then becomes a foreign key.
In this case, if we had another table that described Institutions', then the Institution column in the Instructors table would be a foreign key.
Example
The Instructors table, again.
| Primary Key | Foreign Key? | Alternate Key | |||||||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| |||||||||||||||||||||||||||||||||||||||||||||||
Note
This simplified table contains a number of bad practices, such as the primary and foreign key values used, and naming conventions. We'll get to those.
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