Vladislav Pyatkov created CALCITE-7814:
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Summary: Support the SQL-standard CYCLE clause in recursive CTEs
Key: CALCITE-7814
URL: https://issues.apache.org/jira/browse/CALCITE-7814
Project: Calcite
Issue Type: New Feature
Components: core
Reporter: Vladislav Pyatkov
Add support for the SQL-standard _CYCLE_ clause in recursive common table
expressions, including parsing, validation, relational conversion, and
execution.
_CYCLE_ detects repeated keys within each recursive path and adds cycle-mark
and path columns. A cycle-closing row is returned with its mark set, but does
not produce further recursive expansion.
Example:
{code:sql}
WITH RECURSIVE
edges(src, dst) AS (
VALUES ('A', 'B'), ('B', 'C'), ('C', 'A')
),
walk(node) AS (
VALUES ('A')
UNION ALL
SELECT e.dst
FROM walk w JOIN edges e ON e.src = w.node
)
CYCLE node SET is_cycle TO 'Y' DEFAULT 'N'
USING cycle_path
SELECT node, is_cycle, cycle_path
FROM walk;
{code}
The traversal follows A → B → C → A. The final A is marked as a cycle-closing
row, and recursion stops along that path.
Include execution tests for single and composite cycle keys, negative
validation tests with clear error messages, and a documented example.
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