Getting Started with SQL by Thomas Nield

Author:Thomas Nield
Language: eng
Format: epub, pdf
Publisher: O'Reilly Media, Inc.
Published: 2016-02-23T16:00:00+00:00

SELECT CUSTOMER.CUSTOMER_ID, NAME AS CUSTOMER_NAME FROM CUSTOMER LEFT JOIN CUSTOMER_ORDER ON CUSTOMER.CUSTOMER_ID = CUSTOMER_ORDER.CUSTOMER_ID WHERE ORDER_ID IS NULL

Sure enough, you will only see Rex Tooling Inc and Prairie Construction listed, as they have no orders.

Other JOIN Types

There is a RIGHT JOIN operator, which performs a right outer join that is almost identical to the left outer join. It flips the direction of the join and includes all records from the right table. However, the RIGHT JOIN is rarely used and should be avoided. You should stick to convention and prefer left outer joins with LEFT JOIN, and put the “all records” table on the left side of the join operator.

There also is a full outer join operator called OUTER JOIN that includes all records from both tables. It does a LEFT JOIN and a RIGHT JOIN simultaneously, and can have null records in both tables. It can be helpful to find orphaned records in both directions simultaneously in a single query, but it also is seldom used.

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