BigQuery optimisation query with filtering on nested array of STRUCT fields and grouping back

I'm trying to figure out how to write GQL (Google SQL) query to filter deeply nested structure and after that nest it again and leave first of records for STRUCT properties on the same level with ARRAY.

I prepared a schema sample

 WITH
      Sale AS (
      SELECT
        "1" AS _id,
        STRUCT("11" AS _id,
          "SERVICE" AS feedbackType,
          DATE(TIMESTAMP("2017-01-20 14:05:51.655")) AS createDate) AS serviceFeedback,
        [STRUCT("host" AS key,
          "localhost" AS value),
        STRUCT("location" AS key,
          "Paris" AS value)] AS tags,
        TRUE AS reviewed,
        [STRUCT("1" as saleId, STRUCT("101" AS _id,
            "PRODUCT" AS feedbackType,
            DATE(TIMESTAMP("2017-01-20 14:05:51.655")) AS createDate) AS productFeedback),
        STRUCT("1" as saleId, STRUCT("102" AS _id,
            "PRODUCT" AS feedbackType,
            DATE(TIMESTAMP("2017-01-20 14:06:51.655")) AS createDate) AS productFeedback) ] AS saleItems,
        DATE(TIMESTAMP("2017-01-20 14:05:51.655")) AS latestFeedbackDate )

And a source filter query that flattened all nested fields are required for filtering.

SELECT
  saleId,
  serviceFeedback,
  saleTags,
  reviewed,
  saleItems,
  latestFeedbackDate
FROM (
  SELECT
    sale._id AS saleId,
    serviceFeedback,
    sale.tags AS saleTags,
    reviewed,
    saleItems,
    latestFeedbackDate
  FROM
    `Sale` AS sale,
    sale.saleItems AS saleItems
  WHERE
    reviewed = TRUE
    AND serviceFeedback.createDate >= DATE(TIMESTAMP("2017-01-18 14:05:51.655"))
    AND serviceFeedback._id IS NOT NULL
    AND saleItems.productFeedback.createDate >= DATE(TIMESTAMP("2017-01-18 14:05:51.655")))
ORDER BY
  latestFeedbackDate DESC
LIMIT
  20

The main issue is that after this filtering a want to group all saleItems by sale._id (return the initial structure) and retrieve serviceFeedback field that has type STRUCT.

The expected result in JSON format is:

{
    "saleId":"1",
    "serviceFeedback":{"_id":"11","feedbackType":"SERVICE","createDate":"2017-01-20"},
    "saleTags":[{"key":"host","value":"localhost"},{"key":"location","value":"Paris"}],
    "reviewed":"true",
    "saleItems":[
        {"saleId":"1","productFeedback":{"_id":"101","feedbackType":"PRODUCT","createDate":"2017-01-20"},
        {"saleId":"1","productFeedback":{"_id":"102","feedbackType":"PRODUCT","createDate":"2017-01-20"},
    ],
    "latestFeedbackDate":"2017-01-20"
}

I wrote the simplest idea of query that comes to my mind. It produces the correct result. But probably it's possible to rewrite it more efficient way,

SELECT
  saleId,
  serviceFeedback,
  latestFeedbackDate,
  subQuery.saleItems as saleItems
FROM
  sale
RIGHT JOIN (
  SELECT
    saleId,
    ARRAY_AGG(saleItems) as saleItems
  FROM (
    SELECT
      saleId,
      saleItems
    FROM (
      SELECT
        sale._id AS saleId,
        latestFeedbackDate,
        saleItems
      FROM
        `Sale` AS sale,
        sale.saleItems AS saleItems
      WHERE
        reviewed = TRUE
        AND serviceFeedback.createDate >= DATE(TIMESTAMP("2017-01-18 14:05:51.655"))
        AND serviceFeedback._id IS NOT NULL
        AND saleItems.productFeedback.createDate >= DATE(TIMESTAMP("2017-01-18 14:05:51.655")))
    ORDER BY
      latestFeedbackDate DESC)
  GROUP BY
    saleId
    ) AS subQuery
ON
  sale._id = subQuery.saleId

Could you suggest me a better solution to achieve the same results?

Could you suggest me a better solution to achieve the same results?

Below produces exact same schema as original table and just applies needed filter to saleItems

#standardSQL
SELECT * REPLACE(
  ARRAY(
    SELECT saleItems FROM UNNEST(saleItems) saleItems 
    WHERE reviewed = TRUE
      AND serviceFeedback.createDate >= DATE(TIMESTAMP("2017-01-18 14:05:51.655"))
      AND serviceFeedback._id IS NOT NULL
      AND saleItems.productFeedback.createDate >= DATE(TIMESTAMP("2017-01-18 14:05:51.655"))
  ) AS saleItems)
FROM sale

If you need just subset of fields - use below as an example

#standardSQL
SELECT 
  _id saleId,
  serviceFeedback,
  ARRAY(
    SELECT saleItems FROM UNNEST(saleItems) saleItems 
    WHERE reviewed = TRUE
      AND serviceFeedback.createDate >= DATE(TIMESTAMP("2017-01-18 14:05:51.655"))
      AND serviceFeedback._id IS NOT NULL
      AND saleItems.productFeedback.createDate >= DATE(TIMESTAMP("2017-01-18 14:05:51.655"))
  ) AS saleItems
FROM sale