BigQuery - 相关子查询取消嵌套数组不起作用

Posted 2023-03-24

【中文标题】BigQuery - 相关子查询取消嵌套数组不起作用

【英文标题】：BigQuery - Correlated subquery unnesting array not working

【发布时间】：2020-05-14 11:28:14

【问题描述】：

我正在尝试在 BigQuery 中加入数组元素，但收到以下错误消息：Correlated subqueries that reference other tables are not supported unless they can be de-correlated, such as by transforming them into an efficient JOIN.

假设我有两个映射表：

CREATE OR REPLACE TABLE `test.field_id_name` (
  id STRING,
  name STRING
) AS (
  SELECT * FROM UNNEST(
     [STRUCT("s1", "string1"),
     STRUCT("s2", "string2"),
     STRUCT("s3", "string3")]
  )
)

CREATE OR REPLACE TABLE `test.field_values` (
  id STRING,
  name STRING
) AS (
  SELECT * FROM UNNEST(
     [STRUCT("v1", "val1"),
     STRUCT("v2", "val2"),
     STRUCT("v3", "val3")]
  )
)

我有以下输入：

CREATE OR REPLACE TABLE `test.input` AS
  SELECT [
    STRUCT<id STRING, value ARRAY<STRING>>("s1", ["v1"]),
    STRUCT("s2", ["v1"]),
    STRUCT("s3", ["v1"])
  ] records
  UNION ALL
  SELECT [
    STRUCT("s1", ["v1", "v2"]),
    STRUCT("s2", ["v1", "v2"]),
    STRUCT("s3", ["v1", "v2"])
  ]
  UNION ALL
  SELECT [
    STRUCT("s1", ["v1", "v2", "v3"]),
    STRUCT("s2", ["v1", "v2", "v3"]),
    STRUCT("s3", ["v1", "v2", "v3"])
  ]

我正在尝试产生这个输出：

SELECT [
  STRUCT<id_mapped STRING, value_mapped ARRAY<STRING>>("string1", ["val1"]),
  STRUCT("string2", ["val1"]),
  STRUCT("string3", ["val1"])
] records
UNION ALL
SELECT [
  STRUCT("string1", ["val1", "val2"]),
  STRUCT("string2", ["val1", "val2"]),
  STRUCT("string3", ["val1", "val2"])
]
UNION ALL
SELECT [
  STRUCT("string1", ["val1", "val2", "val3"]),
  STRUCT("string2", ["val1", "val2", "val3"]),
  STRUCT("string3", ["val1", "val2", "val3"])
]

但是，以下查询因相关子查询错误而失败。

SELECT
  ARRAY(
    SELECT
      STRUCT(fin.name, ARRAY(SELECT fv.name FROM UNNEST(value) v JOIN test.field_values fv ON (v = fv.id)))
    FROM UNNEST(records) r
    JOIN test.field_id_name fin ON (fin.id = r.id)
  )
FROM test.input

【问题讨论】：

请提供样本数据和预期结果。

嗨@MikhailBerlyant - 添加了具有所需转换的示例数据

对我来说看起来很乱输入 3) 你到目前为止的代码以及你有什么问题

感谢您的反馈。我已经修改了问题，希望更清楚！

快速浏览 - 现在看起来好多了。以后有时间会仔细看（除非有人已经回答了）：o）

【参考方案1】：

以下是 BigQuery 标准 SQL

#standardSQL
SELECT ARRAY_AGG(STRUCT(id AS id_mapped, val AS value_mapped)) AS records
FROM (
  SELECT fin.name AS id, ARRAY_AGG(fv.name) AS val, FORMAT('%t', t) id1, FORMAT('%t', RECORD) id2
  FROM `test.input` t,
  UNNEST(records) record,
  UNNEST(value) val
  JOIN `test.field_id_name` fin ON record.id = fin.id
  JOIN `test.field_values` fv ON val = fv.id
  GROUP BY id, id1, id2
)
GROUP BY id1   

如果应用于您问题的样本数据 - 返回您期望的准确输出

【讨论】：

不知道你是怎么想出这样的解决方案的。你是魔术师

请考虑对答案进行投票 - 这在 SO 上很重要！ :o) 就像魔术师一样——当你在过去大约 40 多年的时间里日复一日地做这样的事情时——你不会做魔法——你只是机械地应用模式...... :o)