text: -- @testpoint: opengauss关键字Immutable(非保留)，作为函数名,部分测试点合理报错
  
  --关键字不带引号-成功
  drop function if exists Immutable;
  create function Immutable(i integer)
  returns integer
  as $$
  begin
      return i+1;
  end;
  $$ language plpgsql;
  /
  --关键字带双引号-成功
  drop function if exists "Immutable";
  create function "Immutable"(i integer)
  returns integer
  as $$
  begin
      return i+1;
  end;
  $$ language plpgsql;
  /
  --关键字带单引号-合理报错
  drop function if exists 'Immutable';
  create function 'Immutable'(i integer)
  returns integer
  as $$
  begin
      return i+1;
  end;
  $$ language plpgsql;
  /
  --关键字带反引号-合理报错
  drop function if exists `Immutable`;
  create function `Immutable`(i integer)
  returns integer
  as $$
  begin
      return i+1;
  end;
  $$ language plpgsql;
  /
  --清理环境
  drop function if exists immutable(integer);
  drop function if exists "Immutable"(integer);