### Subquery Scan ![[assets/ex_subqueryscan.png|256]] ### The Explain Trace ```sql -- Conceptual plan for a non-inlinable subquery EXPLAIN SELECT * FROM ( SELECT id FROM animals OFFSET 0 -- Prevents pull-up in some versions/cases ) s; ``` ```text Subquery Scan on s (cost=1.00..548.00 rows=20000 width=4) -> Seq Scan on animals (cost=1.00..348.00 rows=20000 width=4) ``` --- - **Description**: Scans the result of a subquery. - **Performance**: High performance; essentially a pass-through node for subqueries that the optimizer cannot flatten into the outer query. - **Factors**: Subquery complexity and the total number of rows processed. - **Cost**: Equivalent to the cost of the child subquery plan. ![[assets/ex_subplan.svg|256]] - **Operates on**: [[Structures/Result Set]] - **Workloads**: - [[Workloads/LWLock/Buffers/BufferContent|LWLock: BufferContent]]