Question

我正在努力了解如何在 cube.js 架构中表示以下类型的 postgres SQL 查询：

SELECT
CASE
    WHEN COUNT(tpp.net_total_amount) > 0 THEN
        SUM(tpp.net_total_amount) / COUNT(tpp.net_total_amount)
    ELSE
        NULL
    END AS average_spend_per_customer
FROM
    (
        SELECT
            SUM(ts.total_amount) AS net_total_amount
        FROM
            postgres.transactions AS ts
        WHERE
            ts.transaction_date >= '2020-11-01' AND
            ts.transaction_date < '2020-12-01'
        GROUP BY
            ts.customer_id,
            ts.event_id
    ) AS tpp
;

我有一种感觉，预聚合可能是我所追求的，但在研究它们之后似乎并非如此。我可以使用以下架构获取每个客户每个事件花费的总金额列表：

cube(`TransactionTotalAmountByCustomerAndEvent`, {
  sql: `SELECT * FROM postgres.transactions`,

  joins: {

  },

  measures: {
    sum: {
      sql: `SUM(total_amount)`,
      type: `number`
    }
  },

  dimensions: {
    eventId: {
      sql: `event_id`,
      type: `string`
    },

    customerId: {
      sql: `customer_id`,
      type: `string`
    },

    transactionDate: {
      sql: `transaction_date`,
      type: `time`
    }
  },

  preAggregations: {
    customerAndEvent: {
      type: `rollup`,
      measureReferences: [sum],
      dimensionReferences: [customerId, eventId]
    }
  }
});

但这实际上只是给了我按客户和事件分组的内部 SELECT 语句的输出。如何查询多维数据集以获取我所追求的每个事件的平均客户支出？

Answer 1

您可能会发现将数据集建模为两个不同的立方体 Customers 和 Transactions 更容易。然后，您需要在多维数据集之间建立连接，然后创建一个特殊维度，并将 subQuery 属性设置为 true。我在下面提供了一个示例来帮助您理解：

cube('Transactions', {
  sql: `SELECT * FROM postgres.transactions`,

  measures: {
    spend: {
      sql: `total_amount`,
      type: `number`,
    },
  },

  dimensions: {
    eventId: {
      sql: `event_id`,
      type: `string`
    },

    customerId: {
      sql: `customer_id`,
      type: `string`
    },

    transactionDate: {
      sql: `transaction_date`,
      type: `time`
    },
  },
})

cube('Customers', {
  sql: `SELECT customer_id FROM postgres.transactions`,

  joins: {
    Transactions: {
      relationship: `hasMany`,
      sql: `${Customers}.id = ${Transactions}.customerId`
    }
  },

  measures: {
    averageSpend: {
      sql: `${spendAmount}`,
      type: `avg`,
    },
  },

  dimensions: {
    id: {
      sql: `customer_id`,
      type: `string`
    },
    spendAmount: {
      sql: `${Transactions.spend}`,
      type: `number`,
      subQuery: true
    },
  }
})

您可以在 Subquery page on the documentation

上找到更多信息

如何在cube.js中实现子查询

1 个答案: