One-to-many

Also written: one-to-many relationship

A link where one row relates to many rows elsewhere, like one leader for many trips; a foreign-key column on the many side is enough.

Not every link needs a table in between. If each trip has exactly one leader, that's one-to-many (one member can lead many trips), and a leader_id column in trips is enough. A link table is for many-to-many, and for facts that belong to the pairing itself, like the role.

Other terms from the same lesson

• composite key: A primary key made of two or more columns together, like (member_id, trip_id).
• database normalization: Splitting data into related tables so each fact is stored exactly once.
• first normal form: The rule that each cell holds one value: no lists or repeated groups squeezed into a column.
• link table: A table whose rows each connect one row of one table to one row of another, plus facts about that connection.
• logical key: The real-world identifier for a row, such as an email or SKU, kept unique even when tables link by an id.
• many-to-many: A relationship where each side can link to many of the other, like members and trips, stored with a link table.
• surrogate key: A key with no meaning outside the database, usually an auto-numbered id, used to link rows while the real-world identifier stays a UNIQUE column.