The expression after ELSE should have the same type as those after THEN: "bigint" is expected but "i

select pc.category_id, 
sum(case when t.so_month between 3 and 5 then t.order_item_num else 0 end) as spring, 
sum(case when t.so_month between 6 and 8 then t.order_item_num else 0 end) as summer, 
sum(case when t.so_month between 9 and 11 then t.order_item_num else 0 end) as autumn, 
sum(case when t.so_month=12 or t.so_month<=2 then t.order_item_num else 0 end) as winnter 
from product_category pc join (select si.product_id, si.order_item_num, month(si.order_create_time) as so_month from so_item si where si.ds between '2013-05-01' and '2014-04-30' and si.is_gift=0) t on pc.product_id=t.product_id 
group by pc.category_id;

select pc.category_id, 
sum(case when t.so_month between 3 and 5 then t.order_item_num else 0L end) as spring, 
sum(case when t.so_month between 6 and 8 then t.order_item_num else 0L end) as summer, 
sum(case when t.so_month between 9 and 11 then t.order_item_num else 0L end) as autumn, 
sum(case when t.so_month=12 or t.so_month<=2 then t.order_item_num else 0L end) as winnter 
from product_category pc join (select si.product_id, si.order_item_num, month(si.order_create_time) as so_month from so_item si where si.ds between '2013-05-01' and '2014-04-30' and si.is_gift=0) t on pc.product_id=t.product_id 
group by pc.category_id;