#pragma once #include #include #include #include namespace DB { class ASTSubquery; class ASTFunction; struct ASTTableExpression; /** Replace subqueries that return exactly one row * ("scalar" subqueries) to the corresponding constants. * * If the subquery returns more than one column, it is replaced by a tuple of constants. * * Features * * A replacement occurs during query analysis, and not during the main runtime, so * the query result can be used for the index in the table. * * Scalar subqueries are executed on the request-initializer server. * The request is sent to remote servers with already substituted constants. */ class ExecuteScalarSubqueriesMatcher { public: using Visitor = InDepthNodeVisitor; struct Data : public WithContext { size_t subquery_depth; Scalars & scalars; Scalars & local_scalars; bool only_analyze; }; static bool needChildVisit(ASTPtr & node, const ASTPtr &); static void visit(ASTPtr & ast, Data & data); private: static void visit(const ASTSubquery & subquery, ASTPtr & ast, Data & data); static void visit(const ASTFunction & func, ASTPtr & ast, Data & data); }; using ExecuteScalarSubqueriesVisitor = ExecuteScalarSubqueriesMatcher::Visitor; }