Outer join
An outer join combines matching rows while preserving unmatched rows from one or both inputs and representing missing counterparts with null values.
DuckDB in Action
A full outer join preserves unmatched rows from both input relations and supplies NULLs on the missing sides.
- How it is used
- Preserves all systems or records when either side may lack optional matching information.
- How deep it goes
- Derives joins from Cartesian products and filtering, then demonstrates full outer join behavior with a small VALUES dataset.
- Examples
- Demonstrates joins over two VALUES relations keyed by id, producing matches and NULL-filled unmatched rows.
- What you can do after
- Apply it via DuckDB SQL to combine relations without discarding keys appearing on only one side.
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.
- How it is used
- Combines complete results from two related tables when matching and unmatched rows from both sides matter.
- How deep it goes
- Defines the result and portability limits, but defers a full query walkthrough and alternative construction.
- Examples
- Uses promotion and orderheader tables to show matching rows and unmatched rows containing nulls.
- What you can do after
- Apply it via SQL to combine two tables while retaining unmatched rows from both inputs.
Read how Learn SQL in a Month of Lunches explains outer join →
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.
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