如下sql里面这一层参数#para(userId)无法注入

select (select user_name from user_info where user_id = #para(userId)) as userName

这样就可以注入进来但是不是字符串

select (select user_name from user_info where user_id = #(userId)) as userName

现有有这样一个情况 我需要注入字符串的参数再select里面的层级 但是参数一直无法注入 求解

select (select user_idfrom user_info where user_name= #para(userName)) as userId