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54 lines
1.8 KiB
C++
54 lines
1.8 KiB
C++
#pragma once
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#include <Parsers/ASTSelectQuery.h>
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#include <Interpreters/DatabaseAndTableWithAlias.h>
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namespace DB
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{
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class Context;
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struct Settings;
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/** Predicate optimization based on rewriting ast rules
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* For more details : https://github.com/ClickHouse/ClickHouse/pull/2015#issuecomment-374283452
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* The optimizer does two different optimizations
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* - Move predicates from having to where
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* - Push the predicate down from the current query to the having of the subquery
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*/
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class PredicateExpressionsOptimizer
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{
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public:
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PredicateExpressionsOptimizer(const Context & context_, const TablesWithColumnNames & tables_with_columns_, const Settings & settings_);
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bool optimize(ASTSelectQuery & select_query);
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private:
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/// Extracts settings, mostly to show which are used and which are not.
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struct ExtractedSettings
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{
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const bool enable_optimize_predicate_expression;
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const bool enable_optimize_predicate_expression_to_final_subquery;
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template<typename T>
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ExtractedSettings(const T & settings_)
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: enable_optimize_predicate_expression(settings_.enable_optimize_predicate_expression),
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enable_optimize_predicate_expression_to_final_subquery(settings_.enable_optimize_predicate_expression_to_final_subquery)
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{}
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};
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const Context & context;
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const std::vector<TableWithColumnNames> & tables_with_columns;
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const ExtractedSettings settings;
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std::vector<ASTs> extractTablesPredicates(const ASTPtr & where, const ASTPtr & prewhere);
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bool tryRewritePredicatesToTables(ASTs & tables_element, const std::vector<ASTs> & tables_predicates);
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bool tryRewritePredicatesToTable(ASTPtr & table_element, const ASTs & table_predicates, const Names & table_column) const;
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bool tryMovePredicatesFromHavingToWhere(ASTSelectQuery & select_query);
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};
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}
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