Fix inconsistent formatting of SELECT ... FROM (EXPLAIN ...)

src/Analyzer/QueryNode.cpp

@@ -421,11 +421,8 @@ ASTPtr QueryNode::toASTImpl(const ConvertToASTOptions & options) const
 
     if (is_subquery)
     {
-        auto subquery = std::make_shared<ASTSubquery>();
-
+        auto subquery = std::make_shared<ASTSubquery>(std::move(result_select_query));
         subquery->cte_name = cte_name;
-        subquery->children.push_back(std::move(result_select_query));
-
         return subquery;
     }
 

src/Analyzer/UnionNode.cpp

@@ -185,11 +185,8 @@ ASTPtr UnionNode::toASTImpl(const ConvertToASTOptions & options) const
 
     if (is_subquery)
     {
-        auto subquery = std::make_shared<ASTSubquery>();
-
+        auto subquery = std::make_shared<ASTSubquery>(std::move(select_with_union_query));
         subquery->cte_name = cte_name;
-        subquery->children.push_back(std::move(select_with_union_query));
-
         return subquery;
     }
 

src/Interpreters/TreeRewriter.cpp

@@ -262,8 +262,7 @@ struct ExistsExpressionData
         select_with_union_query->list_of_selects->children.push_back(std::move(select_query));
         select_with_union_query->children.push_back(select_with_union_query->list_of_selects);
 
-        auto new_subquery = std::make_shared<ASTSubquery>();
-        new_subquery->children.push_back(select_with_union_query);
+        auto new_subquery = std::make_shared<ASTSubquery>(std::move(select_with_union_query));
 
         auto function = makeASTFunction("in", std::make_shared<ASTLiteral>(1u), new_subquery);
         func = *function;

src/Parsers/ASTSelectWithUnionQuery.cpp

@@ -71,8 +71,7 @@ void ASTSelectWithUnionQuery::formatQueryImpl(const FormatSettings & settings, F
             }
             else
             {
-                auto sub_query = std::make_shared<ASTSubquery>();
-                sub_query->children.push_back(*it);
+                auto sub_query = std::make_shared<ASTSubquery>(*it);
                 sub_query->formatImpl(settings, state, frame);
             }
         }

src/Parsers/ASTSubquery.h

@@ -26,6 +26,13 @@ public:
         return clone;
     }
 
+    ASTSubquery() = default;
+
+    ASTSubquery(ASTPtr child)
+    {
+        children.emplace_back(std::move(child));
+    }
+
     void updateTreeHashImpl(SipHash & hash_state, bool ignore_aliases) const override;
     String getAliasOrColumnName() const override;
     String tryGetAlias() const override;

src/Parsers/ExpressionElementParsers.cpp

@@ -123,7 +123,7 @@ bool ParserSubquery::parseImpl(Pos & pos, ASTPtr & node, Expected & expected)
             throw Exception(ErrorCodes::BAD_ARGUMENTS, "EXPLAIN in a subquery cannot have a table function or table override");
 
         /// Replace subquery `(EXPLAIN <kind> <explain_settings> SELECT ...)`
-        /// with `(SELECT * FROM viewExplain("<kind>", "<explain_settings>", SELECT ...))`
+        /// with `(SELECT * FROM viewExplain('<kind>', '<explain_settings>', (SELECT ...)))`
 
         String kind_str = ASTExplainQuery::toString(explain_query.getKind());
 
@@ -141,7 +141,7 @@ bool ParserSubquery::parseImpl(Pos & pos, ASTPtr & node, Expected & expected)
             auto view_explain = makeASTFunction("viewExplain",
                 std::make_shared<ASTLiteral>(kind_str),
                 std::make_shared<ASTLiteral>(settings_str),
-                explained_ast);
+                std::make_shared<ASTSubquery>(explained_ast));
             result_node = buildSelectFromTableFunction(view_explain);
         }
         else
@@ -161,8 +161,7 @@ bool ParserSubquery::parseImpl(Pos & pos, ASTPtr & node, Expected & expected)
         return false;
     ++pos;
 
-    node = std::make_shared<ASTSubquery>();
-    node->children.push_back(result_node);
+    node = std::make_shared<ASTSubquery>(std::move(result_node));
     return true;
 }
 

src/Parsers/ExpressionListParsers.cpp

@@ -225,8 +225,7 @@ static bool modifyAST(ASTPtr ast, SubqueryFunctionType type)
     select_with_union_query->list_of_selects->children.push_back(std::move(select_query));
     select_with_union_query->children.push_back(select_with_union_query->list_of_selects);
 
-    auto new_subquery = std::make_shared<ASTSubquery>();
-    new_subquery->children.push_back(select_with_union_query);
+    auto new_subquery = std::make_shared<ASTSubquery>(std::move(select_with_union_query));
     ast->children[0]->children.back() = std::move(new_subquery);
 
     return true;
@@ -1582,8 +1581,7 @@ public:
         if (!ParserToken(TokenType::ClosingRoundBracket).ignore(pos, expected))
             return false;
 
-        auto subquery = std::make_shared<ASTSubquery>();
-        subquery->children.push_back(std::move(node));
+        auto subquery = std::make_shared<ASTSubquery>(std::move(node));
         elements = {makeASTFunction("exists", subquery)};
 
         finished = true;

src/Parsers/Kusto/ParserKQLQuery.cpp

@@ -576,20 +576,19 @@ bool ParserKQLSubquery::parseImpl(Pos & pos, ASTPtr & node, Expected & expected)
     if (!ParserKQLTableFunction().parse(pos, select_node, expected))
         return false;
 
-    ASTPtr node_subquery = std::make_shared<ASTSubquery>();
-    node_subquery->children.push_back(select_node);
+    ASTPtr node_subquery = std::make_shared<ASTSubquery>(std::move(select_node));
 
     ASTPtr node_table_expr = std::make_shared<ASTTableExpression>();
     node_table_expr->as<ASTTableExpression>()->subquery = node_subquery;
 
     node_table_expr->children.emplace_back(node_subquery);
 
-    ASTPtr node_table_in_select_query_emlement = std::make_shared<ASTTablesInSelectQueryElement>();
-    node_table_in_select_query_emlement->as<ASTTablesInSelectQueryElement>()->table_expression = node_table_expr;
+    ASTPtr node_table_in_select_query_element = std::make_shared<ASTTablesInSelectQueryElement>();
+    node_table_in_select_query_element->as<ASTTablesInSelectQueryElement>()->table_expression = node_table_expr;
 
     ASTPtr res = std::make_shared<ASTTablesInSelectQuery>();
 
-    res->children.emplace_back(node_table_in_select_query_emlement);
+    res->children.emplace_back(node_table_in_select_query_element);
 
     node = res;
     return true;
@@ -618,20 +617,19 @@ bool ParserSimpleCHSubquery::parseImpl(Pos & pos, ASTPtr & node, Expected & expe
             ASTSelectQuery::Expression::TABLES, parent_select_node->as<ASTSelectQuery>()->tables());
     }
 
-    ASTPtr node_subquery = std::make_shared<ASTSubquery>();
-    node_subquery->children.push_back(sub_select_node);
+    ASTPtr node_subquery = std::make_shared<ASTSubquery>(std::move(sub_select_node));
 
     ASTPtr node_table_expr = std::make_shared<ASTTableExpression>();
     node_table_expr->as<ASTTableExpression>()->subquery = node_subquery;
 
     node_table_expr->children.emplace_back(node_subquery);
 
-    ASTPtr node_table_in_select_query_emlement = std::make_shared<ASTTablesInSelectQueryElement>();
-    node_table_in_select_query_emlement->as<ASTTablesInSelectQueryElement>()->table_expression = node_table_expr;
+    ASTPtr node_table_in_select_query_element = std::make_shared<ASTTablesInSelectQueryElement>();
+    node_table_in_select_query_element->as<ASTTablesInSelectQueryElement>()->table_expression = node_table_expr;
 
     ASTPtr res = std::make_shared<ASTTablesInSelectQuery>();
 
-    res->children.emplace_back(node_table_in_select_query_emlement);
+    res->children.emplace_back(node_table_in_select_query_element);
 
     node = res;
     return true;

src/Storages/StorageView.cpp

@@ -251,8 +251,7 @@ void StorageView::replaceWithSubquery(ASTSelectQuery & outer_query, ASTPtr view_
 
     view_name = table_expression->database_and_table_name;
     table_expression->database_and_table_name = {};
-    table_expression->subquery = std::make_shared<ASTSubquery>();
-    table_expression->subquery->children.push_back(view_query);
+    table_expression->subquery = std::make_shared<ASTSubquery>(view_query);
     table_expression->subquery->setAlias(alias);
 
     for (auto & child : table_expression->children)

src/TableFunctions/TableFunctionExplain.cpp

@@ -1,4 +1,5 @@
 #include <Parsers/ASTFunction.h>
+#include <Parsers/ASTSubquery.h>
 #include <Parsers/ASTSelectWithUnionQuery.h>
 #include <Parsers/ParserSetQuery.h>
 #include <Parsers/parseQuery.h>
@@ -21,6 +22,7 @@ namespace ErrorCodes
 {
     extern const int LOGICAL_ERROR;
     extern const int BAD_ARGUMENTS;
+    extern const int UNEXPECTED_AST_STRUCTURE;
 }
 
 namespace
@@ -103,11 +105,25 @@ void TableFunctionExplain::parseArguments(const ASTPtr & ast_function, ContextPt
 
     if (function->arguments->children.size() > 2)
     {
-        const auto & query_arg = function->arguments->children[2];
+        const auto & subquery_arg = function->arguments->children[2];
+        const auto * subquery = subquery_arg->as<ASTSubquery>();
+
+        if (!subquery)
+            throw Exception(ErrorCodes::BAD_ARGUMENTS,
+                "Table function '{}' requires a subquery argument, got '{}'",
+                getName(), queryToString(subquery_arg));
+
+        if (subquery->children.empty())
+            throw Exception(ErrorCodes::UNEXPECTED_AST_STRUCTURE,
+                "A subquery AST element must have a child");
+
+        const auto & query_arg = subquery->children[0];
+
         if (!query_arg->as<ASTSelectWithUnionQuery>())
             throw Exception(ErrorCodes::BAD_ARGUMENTS,
-                "Table function '{}' requires a EXPLAIN SELECT query argument, got EXPLAIN '{}'",
+                "Table function '{}' requires a EXPLAIN's SELECT query argument, got '{}'",
                 getName(), queryToString(query_arg));
+
         explain_query->setExplainedQuery(query_arg);
     }
     else if (kind != ASTExplainQuery::ExplainKind::CurrentTransaction)