Revision as of 07:22, 25 December 2023 edit Ghosts of Europa (talk \| contribs) Extended confirmed users 1,177 edits Rewrite/add material on keys and foreign keys ← Previous edit		Revision as of 07:24, 25 December 2023 edit undo Ghosts of Europa (talk \| contribs) Extended confirmed users 1,177 edits Link to a more specific page on projection Next edit →
Line 39: ==== Foreign Keys ==== A ''foreign key'' is a subset of attributes ''{A}'' in a relation ''R<sub>1</sub>'' that corresponds with a key of another relation ''R<sub>2</sub>'', with the property that the [[Projection (~~mathematics~~relational algebra)\|projection]] of ''R<sub>1</sub>'' on ''{A}'' is a subset of the projection of ''R<sub>2</sub>'' on ''{A}''. In other words, if a tuple in ''R<sub>1</sub>'' contains values for a foreign key, there must be a corresponding tuple in ''R<sub>2</sub>'' containing the same values for the corresponding key.<ref name="professionals"/>{{rp\|34}} === Interpretation ===

Relational model: Difference between revisions