ExternalTablesVisitor via InDepthNodeVisitor

dbms/src/Interpreters/ExpressionAnalyzer.cpp

@@ -242,8 +242,8 @@ void ExpressionAnalyzer::analyzeAggregation()
 void ExpressionAnalyzer::initGlobalSubqueriesAndExternalTables()
 {
     /// Adds existing external tables (not subqueries) to the external_tables dictionary.
-    ExternalTablesVisitor tables_visitor(context, external_tables);
-    tables_visitor.visit(query);
+    ExternalTablesMatcher::Data tables_data{context, external_tables};
+    ExternalTablesVisitor(tables_data).visit(query);
 
     if (do_global)
     {

dbms/src/Interpreters/ExternalTablesVisitor.h

@@ -4,49 +4,43 @@
 #include <Parsers/IAST.h>
 #include <Parsers/ASTIdentifier.h>
 #include <Common/typeid_cast.h>
+#include <Interpreters/InDepthNodeVisitor.h>
 
 namespace DB
 {
 
-/// Finds in the query the usage of external tables (as table identifiers). Fills in external_tables.
-class ExternalTablesVisitor
+/// If node is ASTIdentifier try to extract external_storage.
+class ExternalTablesMatcher
 {
 public:
-    ExternalTablesVisitor(const Context & context_, Tables & tables)
-    :   context(context_),
-        external_tables(tables)
-    {}
-
-    void visit(ASTPtr & ast) const
+    struct Data
     {
-        /// Traverse from the bottom. Intentionally go into subqueries.
-        for (auto & child : ast->children)
-            visit(child);
+        const Context & context;
+        Tables & external_tables;
+    };
 
-        tryVisit<ASTIdentifier>(ast);
+    static constexpr const char * label = "ExternalTables";
+
+    static std::vector<ASTPtr *> visit(ASTPtr & ast, Data & data)
+    {
+        if (auto * t = typeid_cast<ASTIdentifier *>(ast.get()))
+            return visit(*t, ast, data);
+        return {};
     }
 
+    static bool needChildVisit(ASTPtr &, const ASTPtr &) { return true; }
+
 private:
-    const Context & context;
-    Tables & external_tables;
-
-    void visit(const ASTIdentifier & node, ASTPtr &) const
+    static std::vector<ASTPtr *> visit(const ASTIdentifier & node, ASTPtr &, Data & data)
     {
         if (node.special())
-            if (StoragePtr external_storage = context.tryGetExternalTable(node.name))
-                external_tables[node.name] = external_storage;
-    }
-
-    template <typename T>
-    bool tryVisit(ASTPtr & ast) const
-    {
-        if (const T * t = typeid_cast<const T *>(ast.get()))
-        {
-            visit(*t, ast);
-            return true;
-        }
-        return false;
+            if (StoragePtr external_storage = data.context.tryGetExternalTable(node.name))
+                data.external_tables[node.name] = external_storage;
+        return {};
     }
 };
 
+/// Finds in the query the usage of external tables. Fills in external_tables.
+using ExternalTablesVisitor = InDepthNodeVisitor<ExternalTablesMatcher, false>;
+
 }

dbms/src/Interpreters/InDepthNodeVisitor.h

@@ -1,7 +1,6 @@
 #pragma once
 
-#include <unordered_set>
-#include <unordered_map>
+#include <vector>
 #include <Parsers/DumpASTNode.h>
 
 namespace DB