> **Recursive Union** > <table> > <tr> > <td width="25%"><img src="assets/ex_recursiveunion.png"></td> > <td>Orchestrates the execution of recursive Common Table Expressions.</td> > </tr> > </table> > > ```sql > -- Generating a sequence using a recursive CTE > EXPLAIN (ANALYZE, COSTS, BUFFERS, VERBOSE) > WITH RECURSIVE t(n) AS ( > VALUES (1) > UNION ALL > SELECT n+1 FROM t WHERE n < 10 > ) SELECT * FROM t; > ``` > >  > > <!-- literal-explain-plan > Captured EXPLAIN provenance for the adjacent reader-facing visual plan. > Canonical capture metadata lives in scratch/actual_operation_plans.json. > > CTE Scan on t (cost=2.65..3.27 rows=31 width=4) (actual time=0.002..0.006 rows=10 loops=1) > Output: t.n > CTE t > -> Recursive Union (cost=0.00..2.65 rows=31 width=4) (actual time=0.001..0.004 rows=10 loops=1) > -> Result (cost=0.00..0.01 rows=1 width=4) (actual time=0.001..0.001 rows=1 loops=1) > Output: 1 > -> WorkTable Scan on t t_1 (cost=0.00..0.23 rows=3 width=4) (actual time=0.000..0.000 rows=1 loops=10) > Output: (t_1.n + 1) > Filter: (t_1.n < 10) > Rows Removed by Filter: 0 > Planning Time: 0.052 ms > Execution Time: 0.024 ms > --> > > > <!-- > Raw-capture provenance — separate run. > SQL, setup, dataset, settings, and scope: artifacts/chapter4_capture_matrix.json. > Target: PostgreSQL 18.x companion fixture. Cache state: uncontrolled. > Boundary: pg_wait_tracer backend execution root; client states are included when the chart shows them. > Fidelity: exact pg_wait_tracer export. Not the adjacent EXPLAIN run; compare state shape, not durations. > --> > >  > > <table> > <tr> > <td rowspan="2" width="25%"><img src="assets/ex_recursive_union.svg"></td> > <td><b>Performance</b></td><td>Efficiency depends on the recursion depth and the size of the "WorkTable" (the intermediate result set).</td> > </tr> > <tr><td><b>Cost</b></td><td><code>iteration cost * number of iterations</code></td></tr> > </table>