在oracle函数中返回查询(returning query in oracle function)

我是oracle数据库的新手。 尝试创建一个简单的函数，但它返回单引号的完整选择查询。 我不知道为什么。 善意的帮助。 是的！ 它在函数编译结束时也说“提示：nm参数从未使用过”我很困惑。

-- function to return a single letter grade

create or replace function update_grade(nm number) return varchar2
as
grd varchar2(3);
begin
grd := 'select gradeid from grade where nm between marks_s and markks_e';
return grd;
end;
  
  
 
i am new to oracle database. Trying to make a simple function but it is returning complete select query which is in single quotes. I do not know why. kindly help. and yes! it in the end of function compiling also says "hint: nm parameter never used" I am confused. 
 
 
 
  
  
-- function to return a single letter grade

create or replace function update_grade(nm number) return varchar2
as
grd varchar2(3);
begin
grd := 'select gradeid from grade where nm between marks_s and markks_e';
return grd;
end;
  
  
 

                
最满意答案
                
                    
                        
 您没有执行任何查询。 您只是将查询字符串分配给返回的结果变量。 我没有尝试编译它，但是这样的事情： 
 
    create or replace function update_grade(nm number) return varchar2
    as
    grd varchar2(3);
    begin
    SELECT gradeid  INTO grd from grade where nm between marks_s and markks_e;
    return grd;
    end;
 
 如果没有找到数据，您可以考虑为案例添加处理： 
 
   EXCEPTION
      WHEN NO_DATA_FOUND THEN
        grd:= NULL;
You are not executing any query. You are just assigning the query string to the returned result variable. I've not tried to compile it, but something like this:
 
    create or replace function update_grade(nm number) return varchar2
    as
    grd varchar2(3);
    begin
    SELECT gradeid  INTO grd from grade where nm between marks_s and markks_e;
    return grd;
    end;
 
You might consider adding handling for the case when no data is found:
 
   EXCEPTION
      WHEN NO_DATA_FOUND THEN
        grd:= NULL;