Joins

RELATIONSHIP and REQUIRED_RELATIONSHIP, the named joins of Kater SQL.

Call	What it does	Example
`RELATIONSHIP('name', target AS alias ON keys, 'cardinality')`	A named join. Left out when nothing uses it. Cardinality is `one_to_one`, `one_to_many`, `many_to_one` or `many_to_many`.	`LEFT JOIN RELATIONSHIP('customer', kater_dataset.customers AS c ON o.customer_id = c.customer_id, 'many_to_one')`
`REQUIRED_RELATIONSHIP(...)`	The same, kept even when nothing uses it.	`LEFT JOIN REQUIRED_RELATIONSHIP('customer', ...)`