add test

fix

src/Interpreters/NormalizeSelectWithUnionQueryVisitor.cpp

@@ -20,7 +20,7 @@ void NormalizeSelectWithUnionQueryMatcher::getSelectsFromUnionListNode(ASTPtr &
         return;
         }
 
-        selects.push_back(std::move(ast_select));
+        selects.push_back(ast_select);
 }
 
 void NormalizeSelectWithUnionQueryMatcher::visit(ASTPtr & ast, Data & data)
@@ -53,15 +53,16 @@ void NormalizeSelectWithUnionQueryMatcher::visit(ASTSelectWithUnionQuery & ast,
 
         if (union_modes[i] == ASTSelectWithUnionQuery::Mode::ALL)
         {
-            if (auto * inner_union = select_list[i + 1]->as<ASTSelectWithUnionQuery>())
+            if (auto * inner_union = select_list[i + 1]->as<ASTSelectWithUnionQuery>();
+                inner_union && inner_union->union_mode == ASTSelectWithUnionQuery::Mode::ALL)
             {
                 /// Inner_union is an UNION ALL list, just lift up
                 for (auto child = inner_union->list_of_selects->children.rbegin(); child != inner_union->list_of_selects->children.rend();
                      ++child)
-                    selects.push_back(std::move(*child));
+                    selects.push_back(*child);
             }
             else
-                selects.push_back(std::move(select_list[i + 1]));
+                selects.push_back(select_list[i + 1]);
         }
         /// flatten all left nodes and current node to a UNION DISTINCT list
         else if (union_modes[i] == ASTSelectWithUnionQuery::Mode::DISTINCT)
@@ -85,15 +86,23 @@ void NormalizeSelectWithUnionQueryMatcher::visit(ASTSelectWithUnionQuery & ast,
     /// No UNION DISTINCT or only one child in select_list
     if (i == -1)
     {
-        if (auto * inner_union = select_list[0]->as<ASTSelectWithUnionQuery>())
+        if (auto * inner_union = select_list[0]->as<ASTSelectWithUnionQuery>();
+            inner_union && inner_union->union_mode == ASTSelectWithUnionQuery::Mode::ALL)
         {
             /// Inner_union is an UNION ALL list, just lift it up
             for (auto child = inner_union->list_of_selects->children.rbegin(); child != inner_union->list_of_selects->children.rend();
                  ++child)
-                selects.push_back(std::move(*child));
+                selects.push_back(*child);
         }
         else
-            selects.push_back(std::move(select_list[0]));
+            selects.push_back(select_list[0]);
+    }
+
+    /// Just one union type child, lift it up
+    if (selects.size() == 1 && selects[0]->as<ASTSelectWithUnionQuery>())
+    {
+        ast = *(selects[0]->as<ASTSelectWithUnionQuery>());
+        return;
     }
 
     // reverse children list

src/Interpreters/executeQuery.cpp

@@ -480,13 +480,6 @@ static std::tuple<ASTPtr, BlockIO> executeQueryImpl(
         NormalizeSelectWithUnionQueryVisitor::Data data{context.getSettingsRef().union_default_mode};
         NormalizeSelectWithUnionQueryVisitor{data}.visit(ast);
 
-        /// After normalization, if it only has one ASTSelectWithUnionQuery child,
-        /// we can lift it up, this can reduce one unnecessary recursion later in interpreter phase
-        auto select_union = ast->as<ASTSelectWithUnionQuery>();
-        if (select_union && select_union->list_of_selects->children.size() == 1
-            && select_union->list_of_selects->children.at(0)->as<ASTSelectWithUnionQuery>())
-            ast = std::move(select_union->list_of_selects->children.at(0));
-
         query = serializeAST(*ast);
 
         /// Check the limits.
@@ -888,7 +881,7 @@ static std::tuple<ASTPtr, BlockIO> executeQueryImpl(
                 LOG_DEBUG(&Poco::Logger::get("executeQuery"), "Query pipeline:\n{}", msg_buf.str());
             }
         }
-        }
+    }
     catch (...)
     {
         if (!internal)

src/Interpreters/ya.make

@@ -111,6 +111,7 @@ SRCS(
     MetricLog.cpp
     MutationsInterpreter.cpp
     MySQL/InterpretersMySQLDDLQuery.cpp
+    NormalizeSelectWithUnionQueryVisitor.cpp
     NullableUtils.cpp
     OpenTelemetrySpanLog.cpp
     OptimizeIfChains.cpp

tests/queries/0_stateless/01732_explain_syntax_union_query.reference

@@ -0,0 +1,66 @@
+SELECT 1
+UNION ALL
+SELECT 1
+UNION ALL
+SELECT 1
+UNION ALL
+SELECT 1
+UNION ALL
+SELECT 1
+
+SELECT 1
+UNION ALL
+(
+    SELECT 1
+    UNION DISTINCT
+    SELECT 1
+    UNION DISTINCT
+    SELECT 1
+)
+UNION ALL
+SELECT 1
+
+SELECT x
+FROM 
+(
+    SELECT 1 AS x
+    UNION ALL
+    (
+        SELECT 1
+        UNION DISTINCT
+        SELECT 1
+        UNION DISTINCT
+        SELECT 1
+    )
+    UNION ALL
+    SELECT 1
+)
+
+SELECT x
+FROM 
+(
+    SELECT 1 AS x
+    UNION ALL
+    SELECT 1
+    UNION ALL
+    SELECT 1
+)
+
+SELECT 1
+UNION DISTINCT
+SELECT 1
+UNION DISTINCT
+SELECT 1
+
+SELECT 1
+
+
+(
+    SELECT 1
+    UNION DISTINCT
+    SELECT 1
+    UNION DISTINCT
+    SELECT 1
+)
+UNION ALL
+SELECT 1

tests/queries/0_stateless/01732_explain_syntax_union_query.sql

@@ -0,0 +1,86 @@
+EXPLAIN SYNTAX
+SELECT 1
+UNION ALL
+(
+    SELECT 1
+    UNION ALL
+    (
+        SELECT 1
+        UNION ALL
+        SELECT 1
+    )
+    UNION ALL
+    SELECT 1
+);
+
+SELECT ' ';
+
+EXPLAIN SYNTAX
+SELECT 1
+UNION ALL
+(
+    SELECT 1
+    UNION DISTINCT
+    (
+        SELECT 1
+        UNION ALL
+        SELECT 1
+    )
+    UNION ALL
+    SELECT 1
+);
+
+SELECT ' ';
+
+EXPLAIN SYNTAX
+SELECT x
+FROM
+(
+    SELECT 1 AS x
+    UNION ALL
+    (
+        SELECT 1
+        UNION DISTINCT
+        (
+            SELECT 1
+            UNION ALL
+            SELECT 1
+        )
+        UNION ALL
+        SELECT 1
+    )
+);
+
+SELECT ' ';
+
+EXPLAIN SYNTAX
+SELECT x
+FROM 
+(
+    SELECT 1 AS x
+    UNION ALL
+    (
+        SELECT 1
+        UNION ALL
+        SELECT 1
+    )
+);
+
+SELECT ' ';
+
+EXPLAIN SYNTAX
+SELECT 1
+UNION ALL
+SELECT 1
+UNION DISTINCT
+SELECT 1;
+
+SELECT ' ';
+
+EXPLAIN SYNTAX
+(((((((((((((((SELECT 1)))))))))))))));
+
+SELECT ' ';
+
+EXPLAIN SYNTAX
+(((((((((((((((SELECT 1 UNION DISTINCT SELECT 1))) UNION DISTINCT SELECT 1)))) UNION ALL SELECT 1))))))));