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100 lines
3.7 KiB
C++
100 lines
3.7 KiB
C++
#pragma once
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#include <Interpreters/DatabaseAndTableWithAlias.h>
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namespace DB
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{
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class ASTIdentifier;
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class ASTSelectQuery;
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class ASTSubquery;
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class Context;
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/** This class provides functions for Push-Down predicate expressions
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*
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* The Example:
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* - Query before optimization :
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* SELECT id_1, name_1 FROM (SELECT id_1, name_1 FROM table_a UNION ALL SELECT id_2, name_2 FROM table_b)
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* WHERE id_1 = 1
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* - Query after optimization :
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* SELECT id_1, name_1 FROM (SELECT id_1, name_1 FROM table_a WHERE id_1 = 1 UNION ALL SELECT id_2, name_2 FROM table_b WHERE id_2 = 1)
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* WHERE id_1 = 1
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* For more details : https://github.com/yandex/ClickHouse/pull/2015#issuecomment-374283452
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*/
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class PredicateExpressionsOptimizer
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{
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using ProjectionWithAlias = std::pair<ASTPtr, String>;
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using SubqueriesProjectionColumns = std::map<ASTSelectQuery *, std::vector<ProjectionWithAlias>>;
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using IdentifierWithQualifier = std::pair<ASTIdentifier *, String>;
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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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/// QueryNormalizer settings
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const UInt64 max_ast_depth;
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const UInt64 max_expanded_ast_elements;
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const String count_distinct_implementation;
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/// for PredicateExpressionsOptimizer
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const bool enable_optimize_predicate_expression;
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template<typename T>
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ExtractedSettings(const T & settings)
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: max_ast_depth(settings.max_ast_depth),
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max_expanded_ast_elements(settings.max_expanded_ast_elements),
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count_distinct_implementation(settings.count_distinct_implementation),
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enable_optimize_predicate_expression(settings.enable_optimize_predicate_expression)
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{}
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};
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public:
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PredicateExpressionsOptimizer(ASTSelectQuery * ast_select_, ExtractedSettings && settings_, const Context & context_);
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bool optimize();
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private:
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ASTSelectQuery * ast_select;
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const ExtractedSettings settings;
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const Context & context;
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enum OptimizeKind
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{
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NONE,
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PUSH_TO_PREWHERE,
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PUSH_TO_WHERE,
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PUSH_TO_HAVING,
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};
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bool isAggregateFunction(const ASTPtr & node);
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bool isArrayJoinFunction(const ASTPtr & node);
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std::vector<ASTPtr> splitConjunctionPredicate(ASTPtr & predicate_expression);
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std::vector<IdentifierWithQualifier> getDependenciesAndQualifiers(ASTPtr & expression,
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std::vector<DatabaseAndTableWithAlias> & tables_with_aliases);
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bool optimizeExpression(const ASTPtr & outer_expression, ASTPtr & subquery_expression, ASTSelectQuery * subquery);
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bool optimizeImpl(ASTPtr & outer_expression, SubqueriesProjectionColumns & subqueries_projection_columns, OptimizeKind optimize_kind);
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bool canPushDownOuterPredicate(const std::vector<ProjectionWithAlias> & subquery_projection_columns,
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const std::vector<IdentifierWithQualifier> & outer_predicate_dependencies,
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OptimizeKind & optimize_kind);
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void setNewAliasesForInnerPredicate(const std::vector<ProjectionWithAlias> & projection_columns,
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const std::vector<IdentifierWithQualifier> & inner_predicate_dependencies);
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SubqueriesProjectionColumns getAllSubqueryProjectionColumns();
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void getSubqueryProjectionColumns(const ASTPtr & subquery, SubqueriesProjectionColumns & all_subquery_projection_columns);
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ASTs getSelectQueryProjectionColumns(ASTPtr & ast);
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ASTs evaluateAsterisk(ASTSelectQuery * select_query, const ASTPtr & asterisk);
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void cleanExpressionAlias(ASTPtr & expression);
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};
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}
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