Understanding join types

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.
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