IGNITE-29041 docs

docs/_docs/SQL/sql-calcite.adoc

@@ -189,6 +189,52 @@ The new SQL engine mostly inherits data manipulation language (DML) statements s
 
 In most cases, statement syntax is compliant with the old SQL engine. But there are still some differences between DML dialects in H2-based engine and Calcite-based engine. For example, note the `MERGE` statement syntax has changed.
 
+=== Recursive CTEs
+
+The Calcite-based SQL engine supports recursive common table expressions (CTEs) that use `WITH RECURSIVE` and `UNION ALL`.
+Recursive CTEs can be used to express hierarchical traversals, graph-style parent-child walks, and sequence generation queries.
+
+[source,sql]
+----
+WITH RECURSIVE employee_hierarchy (id, manager_id, name, depth) AS (
+    SELECT id, manager_id, name, 0
+    FROM employee
+    WHERE manager_id IS NULL
+
+    UNION ALL
+
+    SELECT e.id, e.manager_id, e.name, h.depth + 1
+    FROM employee e
+    JOIN employee_hierarchy h ON e.manager_id = h.id
+)
+SELECT id, manager_id, name, depth
+FROM employee_hierarchy
+ORDER BY depth, id;
+----
+
+The recursive part can reference the recursive CTE more than once and can contain multiple recursive branches.
+`UNION DISTINCT` recursive CTEs are not supported.
+
+Recursive CTE execution keeps the recursive delta on the query coordinator.
+The delta memory is included into the Calcite query memory quota. See <<memory-quotas>> for details about memory quota configuration.
+
+To protect the cluster from accidentally unbounded recursion, Ignite limits the number of recursive CTE iterations to `100` by default.
+You can change the limit with the `sql.calcite.recursiveCteIterationLimit` distributed property. A negative value disables the limit.
+
+[tabs]
+--
+tab:Unix[]
+[source,shell]
+----
+control.sh --property set --name sql.calcite.recursiveCteIterationLimit --val 1000
+----
+tab:Windows[]
+[source,shell]
+----
+control.bat --property set --name sql.calcite.recursiveCteIterationLimit --val 1000
+----
+--
+
 === Transactions
 
 The Calcite-based SQL engine supports SQL savepoint commands for explicit transactions. See link:sql-reference/transactions[Transactions, window=_blank] for syntax and usage details.

docs/_docs/sql-reference/sql-conformance.adoc

@@ -162,7 +162,7 @@ Ignite does not support the following sub-feature:
 
 `E071–06` Table operators in subqueries
 
-Note that there is no support for non-recursive WITH clause in H2 and Ignite. According to link:http://www.h2database.com/html/grammar.html#with[the H2 docs, window=_blank] there is support for recursive WITH clause, but it fails in Ignite.
+The H2-based SQL engine does not support non-recursive `WITH` clauses. The Calcite-based SQL engine supports recursive CTEs with `WITH RECURSIVE` and `UNION ALL`; see link:SQL/sql-calcite#recursive-ctes[Recursive CTEs, window=_blank].
 
 | E081 Basic Privileges
 | Ignite does not support the following sub-feature: