#pragma once #include #include namespace DB { class Context; struct Settings; /** Predicate optimization based on rewriting ast rules * For more details : https://github.com/ClickHouse/ClickHouse/pull/2015#issuecomment-374283452 * The optimizer does two different optimizations * - Move predicates from having to where * - Push the predicate down from the current query to the having of the subquery */ class PredicateExpressionsOptimizer { public: PredicateExpressionsOptimizer(const Context & context_, const TablesWithColumns & tables_with_columns_, const Settings & settings_); bool optimize(ASTSelectQuery & select_query); private: const bool enable_optimize_predicate_expression; const bool enable_optimize_predicate_expression_to_final_subquery; const Context & context; const TablesWithColumns & tables_with_columns; std::vector extractTablesPredicates(const ASTPtr & where, const ASTPtr & prewhere); bool tryRewritePredicatesToTables(ASTs & tables_element, const std::vector & tables_predicates); bool tryRewritePredicatesToTable(ASTPtr & table_element, const ASTs & table_predicates, Names && table_columns) const; bool tryMovePredicatesFromHavingToWhere(ASTSelectQuery & select_query); }; }