Tiny improvements along the code

- less allocations (potentially)

src/Core/Block.cpp

@@ -623,6 +623,7 @@ NamesAndTypesList Block::getNamesAndTypesList() const
 NamesAndTypes Block::getNamesAndTypes() const
 {
     NamesAndTypes res;
+    res.reserve(columns());
 
     for (const auto & elem : data)
         res.emplace_back(elem.name, elem.type);

src/Interpreters/TreeOptimizer.cpp

@@ -418,7 +418,7 @@ void optimizeDuplicateDistinct(ASTSelectQuery & select)
         return;
 
     std::unordered_set<String> distinct_names = getDistinctNames(*subselect);
-    std::unordered_set<String> selected_names;
+    std::unordered_set<std::string_view> selected_names;
 
     /// Check source column names from select list (ignore aliases and table names)
     for (const auto & id : select.select()->children)
@@ -427,11 +427,11 @@ void optimizeDuplicateDistinct(ASTSelectQuery & select)
         if (!identifier)
             return;
 
-        String name = identifier->shortName();
+        const String & name = identifier->shortName();
         if (!distinct_names.contains(name))
             return; /// Not a distinct column, keep DISTINCT for it.
 
-        selected_names.insert(name);
+        selected_names.emplace(name);
     }
 
     /// select columns list != distinct columns list

src/Storages/SelectQueryInfo.h

@@ -117,10 +117,10 @@ struct InputOrderInfo
      * sort_description_for_merging will be equal to (c, d) and
      * used_prefix_of_sorting_key_size will be equal to 4.
      */
-    size_t used_prefix_of_sorting_key_size;
+    const size_t used_prefix_of_sorting_key_size;
 
-    int direction;
-    UInt64 limit;
+    const int direction;
+    const UInt64 limit;
 
     InputOrderInfo(
         const SortDescription & sort_description_for_merging_,