我有一个类似于这个的存储过程，当我尝试保存它时，我收到了这个错误：
未声明的变量：my_column
CREATE PROCEDURE p (OUT column_param VARCHAR(25))
BEGIN
SELECT my_column INTO coumn_param limit 1;
END;
为什么我不能选择要返回的列？
这是我在程序中的实际查询：
select latitude into lat, longitude into lon
from cities cc
inner join countries c on cc.country_id = c.country_id
inner join regions r on cc.region_id = r.region_id and c.country_id = r.country_id
left join locations l on cc.city_id = l.city_id
where
city = coalesce(cty, city) and
country = coalesce(ctry, country) and
region = coalesce(reg, region)
limit 1;