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
|
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.
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