N1QL 多重连接和求和查询产生错误的输出

Question

我有一个包含以下三个文档的存储桶：

coffee {
    id
}

cold_coffee {
    coffeeId
    number
}

warm_coffee {
    coffeeId
    number
}

我使用 Couchbase Server Community Edition 6.0.0 在 N1QL 中编写了以下查询：

SELECT META(coffee).id as coffeeId,
SUM(cold_coffee.`number`) as `ccNumber`,
SUM(warm_coffee.`number`) as `wcNumber`,
FROM coffee_bucket coffee
left JOIN coffee_bucket cold_coffee
    ON  META(coffee).id = cold_coffee.coffeeId 
    and cold_coffee.type='cold_coffee'
left JOIN coffee_bucket warm_coffee
    ON META(coffee).id = warm_coffee.coffeeId 
    and warm_coffee.type='warm_coffee'
where coffee.type='coffee'
group by META(coffee).id;

我每杯咖啡都有多个 cold_coffee 和 warm_coffee 文档，我需要对所有 cold_coffee 和 warm_coffee 文档的数字求和。我遇到的问题是，例如，如果我有以下文件：

[
    coffee {
        id: 1
    },
    cold_coffee {
        coffeeId:1
        number:5 
    },
    cold_coffee {
        coffeeId:1
        number:5 
    },
    warm_coffee {
        coffeeId:1
        number:10
    }
]

我的总数如下：

ccNumber: 10
wcNumber:20

似乎是因为连接，单个 warm_coffee 文档被计算了两次？

我发现这个 site 可能有同样的错误，但不幸的是它是 SQL。

而且我不确定如何使用 N1QL 解决这个问题，因为 JOIN 的右侧术语必须是 table / bucket，如下面 post.

所示

这是一个可能的 solution 但我不确定如何实现这是 N1QL？

有人可以帮忙吗？

Answer 1

JOINS 可以扩展原来的行。在第一个 Join left 期间，大多数文档被展开。您正在使用第一个文档字段作为第二个连接条件，可以生成多个文档相同的条件。这就是语义的工作原理。您需要根据需要调整加盟条件。

第二个 JOIN 从 LEFT 开始最多使用一个文档。 SUM over DISTINCT 可能不起作用，因为不同文档的相同值（warm_coffee，可能计数不足）被计算一次。如果我是对的，您正在寻找第二次加入以使用来自 LEFT 大多数咖啡的独特文档。

可能你正在寻找这样的东西

SELECT c.coffeeId,
       MAX(c.ccNumber) AS `ccNumber`,
       SUM(warm_coffee.`number`) AS `wcNumber`,
FROM ( SELECT META(coffee).id AS coffeeId,
       SUM(cold_coffee.`number`) AS `ccNumber`
       FROM coffee_bucket coffee
       LEFT JOIN coffee_bucket cold_coffee
            ON  META(coffee).id = cold_coffee.coffeeId AND cold_coffee.type='cold_coffee'
       WHERE coffee.type='coffee'
       GROUP BY META(coffee).id
     ) AS c
LEFT JOIN coffee_bucket warm_coffee
          ON c.coffeeId = warm_coffee.coffeeId AND warm_coffee.type='warm_coffee'
GROUP BY c.coffeeId;

3 级加入

SELECT d.coffeeId,
       MAX(c.ccNumber) AS `ccNumber`,
       MAX(c.wcNumber) AS `wcNumber`,
       SUM(ch.`number`) AS `chNumber`
FROM ( SELECT c.coffeeId,
              MAX(c.ccNumber) AS `ccNumber`,
              SUM(warm_coffee.`number`) AS `wcNumber`,
       FROM ( SELECT META(coffee).id AS coffeeId,
              SUM(cold_coffee.`number`) AS `ccNumber`
              FROM coffee_bucket coffee
              LEFT JOIN coffee_bucket cold_coffee
                   ON  META(coffee).id = cold_coffee.coffeeId AND cold_coffee.type='cold_coffee'
              WHERE coffee.type='coffee'
              GROUP BY META(coffee).id
            ) AS c
       LEFT JOIN coffee_bucket warm_coffee
                 ON c.coffeeId = warm_coffee.coffeeId AND warm_coffee.type='warm_coffee'
       GROUP BY c.coffeeId) AS d
LEFT JOIN coffee_bucket ch
     ON d.coffeeId = ch.coffeeId AND ch.type='chaoc_coffee'
GROUP BY d.coffeeId
;

N1QL 多重连接和求和查询产生错误的输出

N1QL Multiple join and sum query producing wrong output

couchbase

n1ql