text: --  @testpoint:openGauss保留关键字constraint作为 用户名，
  
  --不带引号，合理报错
   CREATE USER constraint PASSWORD 'Bigdata@123';
  
   --加双引号，创建成功
   drop user if exists "constraint";
   CREATE USER "constraint" PASSWORD 'Bigdata@123';
   
   --清理环境
   drop user "constraint";
   
   --加单引号，合理报错
   CREATE USER 'constraint' PASSWORD 'Bigdata@123';
    
   --加反引号，合理报错
   CREATE USER `constraint` PASSWORD 'Bigdata@123';