### Example

    SELECT * FROM order_items \
      LEFT OUTER JOIN orders \
      ON order_items.order_id = orders.id

Joins are typically added to `SELECT` statements to add more columns and records.

### Diagram

    SELECT * FROM `A` INNER JOIN `B`

    ┌────────┐
    │ A  ┌───┼────┐
    │    │ ∩ │    │
    └────┼───┘  B │
         └────────┘

Join | What
--- | ---
Inner join | `∩`
Left outer join | `A` + `∩`
Right outer join | `∩` + `B`
Full outer join | `A` + `∩` + `B`

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