SQL函数：“查询没有结果数据的目标”

我正在研究一个SQL函数应该不会太难的功能：它需要一些参数来在表中查找特定课程，计算该课程的人数，将其与课程的最大容量进行比较，并根据需要返回1或0：

drop function if exists room_for_more_students(the_class_name varchar, the_semester_code int);
create function room_for_more_students(the_class_name varchar, the_semester_code int) 
returns int as $BODY$
begin
    select * from class_offerings as match_table 
    where class_name = the_class_name and semester_code = the_semester_code;
    select count(student_id) from match_table as num_students_in_class;
    select avg(maximum_capacity) from match_table as num_students_allowed_in_class;
    --These will all be the same so "avg" just means "the maximum capacity for the class"
    if  num_students_in_class < num_students_allowed_in_class then return 1;
    else return 0;
    end if;
end
$BODY$
language plpgsql;

---

我尝试过用PERFORM来代替，但我尝试的任何组合似乎要么保留了相同的问题，要么创造了大量新的问题。我也对此做了一些研究，因为还有其他一些关于同一问题的帖子，但大多数时候答案似乎是用户没有添加具体的返回语句，我已经添加了。我完全没有主意了，如果有任何可能的输入，我将不胜感激。

对于您的情况，您必须声明一些变量并将其与查询结果一起分配。如果不将查询结果分配给nowhere，则无法运行查询

我更新您的功能如下：

drop function if exists room_for_more_students(the_class_name varchar, the_semester_code int); create function room_for_more_students(the_class_name varchar, the_semester_code int) returns int as $BODY$ DECLARE num_students_allowed_in_class numeric; num_students_in_class numeric; begin WITH match_table AS ( select * from class_offerings where class_name = the_class_name and semester_code = the_semester_code ) select count(student_id), avg(maximum_capacity) INTO num_students_in_class, num_students_allowed_in_class from match_table; if num_students_in_class 希望它符合你的要求

添加return查询，并在它之后放入您想要返回的内容 drop function if exists room_for_more_students(the_class_name varchar, the_semester_code int); create function room_for_more_students(the_class_name varchar, the_semester_code int) returns int as $BODY$ DECLARE num_students_allowed_in_class numeric; num_students_in_class numeric; begin WITH match_table AS ( select * from class_offerings where class_name = the_class_name and semester_code = the_semester_code ) select count(student_id), avg(maximum_capacity) INTO num_students_in_class, num_students_allowed_in_class from match_table; if num_students_in_class