diff --git a/lib/rubocop/cop/isucon/mixin/mysql2_methods.rb b/lib/rubocop/cop/isucon/mixin/mysql2_methods.rb
index 0c0f7440..8c5d6221 100644
--- a/lib/rubocop/cop/isucon/mixin/mysql2_methods.rb
+++ b/lib/rubocop/cop/isucon/mixin/mysql2_methods.rb
@@ -9,17 +9,19 @@ module Mysql2Methods
           extend NodePattern::Macros
 
           def_node_search :find_xquery, <<~PATTERN
-            (send (send nil? _) {:xquery | :query} (${str dstr} $...) ...)
+            (send (send nil? _) {:xquery | :query} (${str dstr lvar ivar cvar} $...) ...)
           PATTERN
 
           # @param node [RuboCop::AST::Node]
           # @yieldparam type [Symbol] Node type. one of `:str`, `:dstr`
-          # @yieldparam root_gda [RuboCop::Isucon::GDA::Client]
+          # @yieldparam root_gda [RuboCop::Isucon::GDA::Client,nil]
+          #
+          # @note If arguments of `db.xquery` isn't string, `root_gda` is `nil`
           def with_xquery(node)
             find_xquery(node) do |type, params|
               sql = xquery_param(type: type, params: params)
 
-              root_gda = RuboCop::Isucon::GDA::Client.new(sql)
+              root_gda = sql ? RuboCop::Isucon::GDA::Client.new(sql) : nil
 
               yield type, root_gda
             end
diff --git a/lib/rubocop/cop/isucon/mysql2/n_plus_one_query.rb b/lib/rubocop/cop/isucon/mysql2/n_plus_one_query.rb
index 5d3e62aa..f0d81034 100644
--- a/lib/rubocop/cop/isucon/mysql2/n_plus_one_query.rb
+++ b/lib/rubocop/cop/isucon/mysql2/n_plus_one_query.rb
@@ -31,6 +31,8 @@ module Mysql2
         #   SQL
         #
         class NPlusOneQuery < Base
+          include Mixin::Mysql2Methods
+
           MSG = "This looks like N+1 query."
 
           # @see https://github.com/rubocop/rubocop-performance/blob/v1.11.5/lib/rubocop/cop/performance/collection_literal_in_loop.rb#L38
@@ -42,10 +44,6 @@ class NPlusOneQuery < Base
           # @see https://github.com/rubocop/rubocop-performance/blob/v1.11.5/lib/rubocop/cop/performance/collection_literal_in_loop.rb#L41
           ENUMERABLE_METHOD_NAMES = (Enumerable.instance_methods + [:each]).to_set.freeze
 
-          def_node_search :find_xquery, <<-PATTERN
-            (send (send nil? _) {:xquery | :query} ...)
-          PATTERN
-
           def_node_matcher :csv_loop?, <<~PATTERN
             (block
               (send (const nil? :CSV) :parse ...)
@@ -68,7 +66,7 @@ class NPlusOneQuery < Base
 
           # @param node [RuboCop::AST::Node]
           def on_send(node)
-            find_xquery(node) do
+            with_xquery(node) do |_type, _root_gda|
               receiver, = *node.children
 
               next if !receiver.send_type? || !parent_is_loop?(receiver)