Merge pull request #40387 from jhawthorn/exists_on_contradiction

Avoid query from exists? on contradictory relation

activerecord/lib/active_record/relation/finder_methods.rb

@@ -315,6 +315,7 @@ def exists?(conditions = :none)
       end
 
       relation = construct_relation_for_exists(conditions)
+      return false if relation.where_clause.contradiction?
 
       skip_query_cache_if_necessary { connection.select_rows(relation.arel, "#{name} Exists?").size == 1 }
     end

activerecord/test/cases/relation_test.rb

@@ -444,6 +444,18 @@ def test_marshal_load_legacy_relation
       end
     end
 
+    test "no queries on empty relation exists?" do
+      assert_queries(0) do
+        Post.where(id: []).exists?(123)
+      end
+    end
+
+    test "no queries on empty condition exists?" do
+      assert_queries(0) do
+        Post.all.exists?(id: [])
+      end
+    end
+
     private
       def skip_if_sqlite3_version_includes_quoting_bug
         if sqlite3_version_includes_quoting_bug?