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Merge pull request #579 from sakirr05/week5-coreNumbers
week 5: coreNumbers
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‎doc/metrics/pgr_coreNumbers.rst‎

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.. rubric:: Availability
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.. rubric:: Version 4.1.0
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* Version 4.1.0
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* New experimental function.
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* New experimental function.
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Description
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-------------------------------------------------------------------------------
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The **core number** of a vertex is the largest value :math:`k` such that the
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vertex belongs to the :math:`k`-core of the graph.
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**The main characteristics are:**
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The :math:`k`-core of a graph is the maximal subgraph in which every vertex has
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degree at least :math:`k`. K-core decomposition assigns one core number to each
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vertex and is widely used in network analysis to identify densely connected
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regions and hierarchical structure.
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- Works for **undirected** graphs.
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- Each vertex has **exactly one** core number.
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- **All vertices** in the graph are returned.
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- The number of result rows is :math:`|V|`.
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- Two or more vertices can share the same core number.
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- The result is ordered by ``node`` ascending.
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This implementation works for **undirected** graphs. Each vertex has exactly one
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core number, all vertices in the graph are returned, and the number of result
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rows is :math:`|V|`. Two or more vertices can share the same core number. The
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result is ordered by ``node`` ascending.
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- Running time: :math:`O(m)`
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|Boost| Boost Graph Inside
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.. rubric:: References
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* Batagelj, V. and Zaversnik, M. (2003). An O(m) Algorithm for Cores Decomposition
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of Networks. arXiv:cs/0310049.
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Signatures
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-------------------------------------------------------------------------------
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-------------------------------------------------------------------------------
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.. list-table::
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:width: 81
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:widths: auto
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:header-rows: 1
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* - Column
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- Type
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- Description
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* - ``seq``
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- ``BIGINT``
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- Sequential value starting from 1.
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* - ``node``
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- ``BIGINT``
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- Identifier of the vertex.
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* - ``core``
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- ``BIGINT``
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- Core number of the vertex.
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:width: 81
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:widths: auto
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:header-rows: 1
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* - Column
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- Type
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- Description
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* - ``seq``
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- ``BIGINT``
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- Sequential value starting from 1.
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* - ``node``
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- ``BIGINT``
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- Identifier of the vertex.
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* - ``core``
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- ``BIGINT``
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- Core number of the vertex.
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See Also
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-------------------------------------------------------------------------------
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* :doc:`sampledata`
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* :doc:`pgr_betweennessCentrality`
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* :doc:`metrics-family`
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.. rubric:: Indices and tables

‎pgtap/metrics/coreNumbers/edge_cases.pg‎

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/* :file: This file is part of the pgRouting project.
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:copyright: Copyright (c) 2026-2026 pgRouting developers
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:license: Creative Commons Attribution-Share Alike 3.0 https://creativecommons.org/licenses/by-sa/3.0 */
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BEGIN;
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UPDATE edges SET cost = sign(cost), reverse_cost = sign(reverse_cost);
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SELECT CASE WHEN NOT min_version('4.1.0') THEN plan(1) ELSE plan(9) END;
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CREATE OR REPLACE FUNCTION edge_cases()
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RETURNS SETOF TEXT AS
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$BODY$
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BEGIN
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IF NOT min_version('4.1.0') THEN
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RETURN QUERY
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SELECT skip(1, 'Function is new on 4.1.0');
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RETURN;
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END IF;
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PREPARE idless2_q AS
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SELECT node, core FROM pgr_coreNumbers(
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'SELECT id, source, target, cost, reverse_cost
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FROM edges WHERE id < 2'
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) ORDER BY node;
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PREPARE idless2_r AS
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SELECT * FROM (VALUES
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(5::BIGINT, 1::BIGINT),
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(6, 1))
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AS t(node, core);
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RETURN QUERY
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SELECT lives_ok('idless2_q');
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RETURN QUERY
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SELECT results_eq('idless2_q', 'idless2_r');
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PREPARE idless4_q AS
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SELECT node, core FROM pgr_coreNumbers(
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'SELECT id, source, target, cost, reverse_cost
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FROM edges WHERE id < 4'
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) ORDER BY node;
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PREPARE idless4_r AS
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SELECT * FROM (VALUES
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(5::BIGINT, 1::BIGINT),
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(6, 1),
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(10, 1),
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(15, 1))
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AS t(node, core);
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RETURN QUERY
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SELECT lives_ok('idless4_q');
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RETURN QUERY
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SELECT results_eq('idless4_q', 'idless4_r', 'test 4');
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PREPARE idless5_q AS
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SELECT node, core FROM pgr_coreNumbers(
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'SELECT id, source, target, cost, reverse_cost
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FROM edges WHERE id < 5'
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) ORDER BY node;
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PREPARE idless5_r AS
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SELECT * FROM (VALUES
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(5::BIGINT, 1::BIGINT),
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(6, 1),
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(7, 1),
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(10, 1),
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(15, 1))
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AS t(node, core);
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RETURN QUERY
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SELECT lives_ok('idless5_q');
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RETURN QUERY
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SELECT results_eq('idless5_q', 'idless5_r', 'test 6');
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PREPARE idless10_q AS
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SELECT node, core FROM pgr_coreNumbers(
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'SELECT id, source, target, cost, reverse_cost
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FROM edges WHERE id < 10'
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) ORDER BY node;
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PREPARE idless10_r AS
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SELECT * FROM (VALUES
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(1::BIGINT, 1::BIGINT),
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(3, 1),
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(5, 1),
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(6, 2),
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(7, 2),
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(10, 2),
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(11, 2),
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(15, 1),
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(16, 1))
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AS t(node, core);
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RETURN QUERY
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SELECT lives_ok('idless10_q');
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RETURN QUERY
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SELECT results_eq('idless10_q', 'idless10_r', 'test 8');
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PREPARE empty_q AS
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SELECT node, core FROM pgr_coreNumbers(
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'SELECT id, source, target, cost, reverse_cost
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FROM edges WHERE id < 0'
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) ORDER BY node;
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RETURN QUERY
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SELECT is_empty('empty_q', 'Empty graph returns no rows');
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END;
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$BODY$
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LANGUAGE plpgsql;
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SELECT edge_cases();
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SELECT finish();
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ROLLBACK;

‎pgtap/metrics/coreNumbers/inner_query.pg‎

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/* :file: This file is part of the pgRouting project.
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:copyright: Copyright (c) 2026-2026 pgRouting developers
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:license: Creative Commons Attribution-Share Alike 3.0 https://creativecommons.org/licenses/by-sa/3.0 */
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BEGIN;
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UPDATE edges SET cost = sign(cost), reverse_cost = sign(reverse_cost);
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SELECT CASE WHEN NOT min_version('4.1.0') THEN plan(1) ELSE plan(54) END;
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CREATE OR REPLACE FUNCTION inner_query()
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RETURNS SETOF TEXT AS
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$BODY$
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BEGIN
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IF NOT min_version('4.1.0') THEN
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RETURN QUERY
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SELECT skip(1, 'Function is new on 4.1.0');
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RETURN;
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END IF;
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RETURN QUERY
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SELECT style_dijkstra('pgr_coreNumbers(', ')');
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END;
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$BODY$
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LANGUAGE plpgsql;
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SELECT inner_query();
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SELECT finish();
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ROLLBACK;

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