The join type determines what records are selected from two related tables. There are three join types:
- One-to-one (or one-to-many): a record is only pulled if the key exists both in the primary and the foreign table.
- Left join: each record is pulled from the left table, even if there is no corresponding key in the right table.
- Right join: each record is pulled from the right table, even there is no corresponding key in the left table.