MySql - 从一张表的两组记录中获取总数[重复]

Question

我使用的是 Mysql 5.5 版。我有两个表 - 产品，订单。

CREATE TABLE `product` (
  `id` int(11) NOT NULL,
  `name` varchar(45) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE `ordr` (
  `id` int(11) NOT NULL,
  `product_id` varchar(45) DEFAULT NULL,
  `status` varchar(45) DEFAULT NULL,
  `qty` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

这是它们的填充方式 -

insert into product values (20, 'pen');

insert into ordr values (100, 20, 'queue', 5);
insert into ordr values (110, 20, 'queue', 5);
insert into ordr values (120, 20, 'pending', 10);
insert into ordr values (130, 20, 'pending', 10);
insert into ordr values (140, 20, 'pending', 10);

我想获取处于两种不同状态的产品的总数。对于上面数据的测试数据，我希望看到队列数量为 10，待处理数量为 30。

当我跑步时

select p.name, sum(o.qty) as queue_qty, sum(o2.qty) as pending_qty
from product p
left outer join ordr o on o.product_id = p.id and o.status = 'queue'
left outer join ordr o2 on o2.product_id = p.id and o2.status = 'pending'
where p.id = 20;

我明白了

name - pen
queue_qty - 30
pending_qty - 60

有人可以帮我修复这个 SQL 吗？

Answer 1

您需要在加入之前汇总信息。由于您有两个 1-n 关系，因此您的连接逻辑是重复信息。

select
  p.name
  , o.qty as qty_queue
  , o2.qty as qty_pending
from
  product p
  join (
    select
      product_id
      , sum(qty) as qty
    from
      ordr
    where
      ordr.status = 'queue'
    group by
      product_id
  ) o
    on p.id = o.product_id
  join (
    select
      product_id
      , sum(qty) as qty
    from
      ordr
    where
      ordr.status = 'pending'
    group by
      product_id
  ) o2
    on p.id = o2.product_id
group by
  p.name