存储过程中的sql

下面的存储过程中的sql为什么单独可以执行，放到存储过程里面就不能执行了？

--创建表
create table demo(id int,name varchar(20),quarter int,nums int,amunt_sold decimal(8,2)); 
insert into demo values(1, 'a',1, 1000,200); 
insert into demo values(2, 'a',2, 2000,100.12); 
insert into demo values(3, 'a',3, 4000,156); 
insert into demo values(4, 'b',1, 5000,234); 
insert into demo values(5, 'b',3, 3000,345); 
insert into demo values(6, 'c',3, 3500,222); 
insert into demo values(7, 'd',1, 4200,111); 
insert into demo values(8, 'd',2, 5500,555);

--创建存储过程
DROP PROCEDURE IF EXISTS mtest;
create procedure mtest()
RETURNS set(row(x varchar(8000),a varchar(8000),b varchar(8000),c varchar(8000),d varchar(8000)) NOT null);
define sql2 set(row(x varchar(8000),a varchar(8000),b varchar(8000),c varchar(8000),d varchar(8000)) NOT null);
INSERT INTO table(sql2)  
select * from (select name,nums,id from demo) 
PIVOT (sum(nums) for name 
in('a','b','c','d'));
RETURN sql2;
END PROCEDURE;

--调用
CALL mtest();