如何编写一个 n1ql 查询来对同一存储桶中多个文档的值求和

Question

我是 Couchbase 数据库服务器的新手，我试图用一个查询来实现我用三个查询所做的事情，因为这效率不高。

我在同一个存储桶中有三种不同的文档类型 (x,y,z)；都有一个相似的键：'district' 像这样：

文档 x:

{
  "type": "x",
  "district": "Some district"
}

文档 y:

{
  "type": "y",
  "district": "Some district"
}

文档 z:

{
  "type": "z",
  "district": "Some district"
}

我目前在 PHP 中实现了类似于以下伪代码的东西：

$totalDistrictInX = "SELECT COUNT(x) FROM bucket WHERE type = 'x' AND district = 'Maboro';

$totalDistrictInY = "SELECT COUNT(x) FROM bucket WHERE type = 'y' AND district = 'Maboro';

$totalDistrictInZ = "SELECT COUNT(x) FROM bucket WHERE type = 'z' AND district = 'Maboro';

$totalCountOfMaboro = $totalDistrictInX + $totalDistrictInY + $totalDistrictInZ;

我无法使用 JOIN 查询，因为当前使用的 Couchbase 服务器低于 5.50 which only supports joining documents between document key to document field and not between document fields。

有没有办法通过一个 n1ql 查询来实现这一点？如有任何帮助，我们将不胜感激。

Answer 1

GROUP BY 和 COUNT 组合可以成为您的解决方案吗？

SELECT COUNT(x) FROM bucket WHERE district = 'Maboro' GROUP BY type

Documentation

Answer 2

使用不带group by的聚合查询来统计总数，通过predicate控制统计哪些文档。

SELECT COUNT(1) AS cnt
FROM bucket
WHERE type IN ['x', 'y', 'z'] AND district = 'Maboro';

如果您需要对每种类型进行计数，请使用 GROUP BY

SELECT type, COUNT(1) AS cnt
FROM bucket
WHERE type IN ['x', 'y', 'z'] AND district = 'Maboro'
GROUP BY type;

如果你想要总数和单个类型，它算作数组

SELECT ARRAY_SUM(av[*].cnt) AS totalcnt, av AS details
LET av = (SELECT type, COUNT(1) AS cnt
          FROM bucket
          WHERE type IN ['x', 'y', 'z'] AND district = 'Maboro'
          GROUP BY type);

如何编写一个 n1ql 查询来对同一存储桶中多个文档的值求和

How to write one n1ql query to sum values from multiple documents in the same bucket

couchbase

n1ql