在多个表中双重分组

Question

我有三个连接的表。

select * 
from Ordering 
inner join Client on client.id=ordering.client_id 
inner join Dish on ordering.dish_id=dish.id

我想按name_dish和后来的client_id对总quantity列和分组。

现在我做到了，但这还不够（对于一个客户）：

select client.familyName, client.name, client.phone, sum(ordering.quantity),dish.name_dish 
from Ordering 
inner join Client on client.id=ordering.client_id 
inner join Dish on ordering.dish_id=dish.id 
where ordering.client_id=1 
group by (dish.name_dish)

Answer 1

从现有查询开始，您需要将不在聚合 function 中的所有select ed 列放在group by子句中（即除quantity之外的所有列）。 我还建议包括client和dish桌的主键，以防两个客户端（分别是菜）具有相同的名称。

考虑以下聚合查询：

select c.family_name, c.name, c.phone, sum(o.quantity) sum_quantity, d.name_dish
from ordering o
inner join client c on c.id = o.client_id 
inner join dish d on o.dish_id = d.id
group by c.client_id, c.family_name, c.name, c.phone, d.id, d.name_dish

一些数据库（实际上是 Postgres）只满足group by子句中两个表的主键：

select c.family_name, c.name, c.phone, sum(o.quantity) sum_quantity, d.name_dish
from ordering o
inner join client c on c.id = o.client_id 
inner join dish d on o.dish_id = d.id
group by c.client_id, d.id