SQL joins cheatsheet

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.

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