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RecursiveCTE.h
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51 lines (43 loc) · 1.78 KB
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#pragma once
#include <Core/NamesAndTypes.h>
#include <Interpreters/DatabaseCatalog.h>
#include <Analyzer/IQueryTreeNode.h>
#include <Analyzer/TableNode.h>
namespace DB
{
/** Recursive CTEs allow to recursively evaluate UNION subqueries.
*
* Overview:
* https://www.postgresql.org/docs/current/queries-with.html#QUERIES-WITH-RECURSIVE
*
* Current implementation algorithm:
*
* During query analysis, when we resolve UNION node that is inside WITH RECURSIVE section of parent query we:
* 1. First resolve non recursive subquery.
* 2. Create temporary table using projection columns of resolved subquery from step 1.
* 3. Create temporary table expression node using storage from step 2.
* 4. Create resolution scope for recursive subquery. In that scope we add node from step 3 as expression argument with UNION node CTE name.
* 5. Resolve recursive subquery.
* 6. If in resolved UNION node temporary table expression storage from step 2 is used, we update UNION query with recursive CTE table.
*
* During query planning if UNION node contains recursive CTE table, we add ReadFromRecursiveCTEStep to query plan. That step is responsible for whole
* recursive CTE query execution.
*
* TODO: Improve locking in ReadFromRecursiveCTEStep.
* TODO: Improve query analysis if query contains aggregates, JOINS, GROUP BY, ORDER BY, LIMIT, OFFSET.
* TODO: Support SEARCH DEPTH FIRST BY, SEARCH BREADTH FIRST BY syntax.
* TODO: Support CYCLE syntax.
* TODO: Support UNION DISTINCT recursive CTE mode.
*/
class RecursiveCTETable
{
public:
RecursiveCTETable(TemporaryTableHolderPtr holder_,
StoragePtr storage_,
NamesAndTypes columns_);
StorageID getStorageID() const;
TemporaryTableHolderPtr holder;
StoragePtr storage;
NamesAndTypes columns;
};
}