How deeply does Learn SQL in a Month of Lunches cover outer join?

Defines the result and portability limits, but defers a full query walkthrough and alternative construction.

Outer join

As explained in Learn SQL in a Month of Lunches

A full outer join returns matching rows and preserves unmatched rows from both joined inputs, filling missing columns with null values.

An outer join keeps rows that do not have a matching value in the other table. A full outer join keeps unmatched rows from both tables, filling missing columns with null values. section 9.2 section 9.2.4

Keep every promotion and every order

SELECT p.PromotionCode, oh.OrderID FROM promotion p FULL OUTER JOIN orderheader oh ON p.PromotionID = oh.PromotionID; A promotion without an order appears with a null OrderID; an order without a matching promotion appears with a null PromotionCode. Matching rows contain values from both tables. section 9.2.4

Choose the join type according to which unmatched rows matter:

Use LEFT JOIN to preserve every row from the left table. section 9.2.4
Use RIGHT JOIN to preserve every row from the right table. section 9.2.3
Use FULL OUTER JOIN when both tables must contribute unmatched rows. section 9.2.4

FULL JOIN may be accepted as a shorter spelling, but support varies by database system. MySQL, MariaDB, and SQLite do not support this join type here. section 9.2.4

How Learn SQL in a Month of Lunches covers it

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Also explained in

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DuckDB in ActionA full outer join preserves unmatched rows from both input relations and supplies NULLs on the missing sides.

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Related concepts

joinkind of · A join is an operation that combines records or rows from multiple data sources according to specified matching conditions or relationships.
Hibernateused by · Hibernate is a Java object-relational mapping and persistence framework that maps application objects to relational database data.
inner joincontrasts with · An inner join is a relational operation that returns combinations of rows only when the join condition matches records in both input relations.

This explainer was generated by Manning's knowledge graph from the text of Learn SQL in a Month of Lunches. The section links point to the parts of the book it draws on.